From cce2a4f700158fe3809dd76cf5084609d9c50901 Mon Sep 17 00:00:00 2001
From: John Kerl <kerl.john.r@gmail.com>
Date: Sun, 28 Feb 2021 10:14:32 -0500
Subject: [PATCH] Port fraction verb from C to Go

---
 go/cases-to-do.txt                            |   1 -
 go/gg                                         |  35 +-
 go/reg-test/cases/case-c-verb-fraction.sh     |  15 -
 go/reg-test/cases/case-verb-fraction.sh       |  15 +
 .../expected/case-c-verb-fraction.sh.out      | 145 ---
 go/reg-test/expected/case-cli-help.sh.out     | 115 ++-
 .../expected/case-verb-fraction.sh.out        | 909 ++++++++++++++++++
 go/src/cli/mlrcli_transformers.go             |   7 +-
 go/src/transformers/fraction.go               | 278 ++++++
 go/src/types/mlrval_accessors.go              |   4 +
 go/src/types/mlrval_functions_booleans.go     |  10 +-
 go/todo.txt                                   |   1 +
 12 files changed, 1288 insertions(+), 247 deletions(-)
 delete mode 100644 go/reg-test/cases/case-c-verb-fraction.sh
 create mode 100644 go/reg-test/cases/case-verb-fraction.sh
 delete mode 100644 go/reg-test/expected/case-c-verb-fraction.sh.out
 create mode 100644 go/reg-test/expected/case-verb-fraction.sh.out
 create mode 100644 go/src/transformers/fraction.go

diff --git a/go/cases-to-do.txt b/go/cases-to-do.txt
index a06c32294..b0b92f1cd 100644
--- a/go/cases-to-do.txt
+++ b/go/cases-to-do.txt
@@ -92,7 +92,6 @@ rrv ./reg-test/cases/case-c-format-values.sh
 rrv ./reg-test/cases/case-c-fraction.sh
 rrv ./reg-test/cases/case-c-having-fields.sh
 rrv ./reg-test/cases/case-c-head-early-out.sh
-rrv ./reg-test/cases/case-c-histogram.sh
 rrv ./reg-test/cases/case-c-in-place-processing.sh
 rrv ./reg-test/cases/case-c-int-float-stats1-step1.sh
 rrv ./reg-test/cases/case-c-join-prepipe.sh
diff --git a/go/gg b/go/gg
index 1e5e18b0c..93db9424f 100755
--- a/go/gg
+++ b/go/gg
@@ -52,39 +52,6 @@ mention() {
 
 # ================================================================
 
-run_mlr --from r put -q '
-  a = 1;
-  b = 2;
-  print;
-  print "OUT1a ". a;
-  print "OUT1b ". b;
-  if (NR == 1) {
-    a = 3;
-    c = 4;
-    print "IN1a  ". a;
-    print "IN1c  ". c;
-  } else {
-    b = 5;
-    d = 6;
-    print "IN2a  ". b;
-    print "IN2c  ". d;
-  }
-  print "OUT2a ". a;
-  print "OUT2a ". b;
-'
-
-# OUT1a 1
-# OUT1b 2
-# IN1a  3
-# IN1c  4
-# OUT2a 3
-# OUT2a 2
-#
-# OUT1a 1
-# OUT1b 2
-# IN2a  5
-# IN2c  6
-# OUT2a 1
-# OUT2a 5
+run_mlr --oxtab fraction -f x,y -g a -p -c ./reg-test/input/abixy-het
 
 # ================================================================
diff --git a/go/reg-test/cases/case-c-verb-fraction.sh b/go/reg-test/cases/case-c-verb-fraction.sh
deleted file mode 100644
index 686d4bc1a..000000000
--- a/go/reg-test/cases/case-c-verb-fraction.sh
+++ /dev/null
@@ -1,15 +0,0 @@
-run_mlr fraction -f x,y              $indir/abixy-het
-run_mlr fraction -f x,y -g a         $indir/abixy-het
-run_mlr fraction -f x,y -g a,b       $indir/abixy-het
-
-run_mlr fraction -f x,y        -p    $indir/abixy-het
-run_mlr fraction -f x,y -g a   -p    $indir/abixy-het
-run_mlr fraction -f x,y -g a,b -p    $indir/abixy-het
-
-run_mlr fraction -f x,y           -c $indir/abixy-het
-run_mlr fraction -f x,y -g a      -c $indir/abixy-het
-run_mlr fraction -f x,y -g a,b    -c $indir/abixy-het
-
-run_mlr fraction -f x,y        -p -c $indir/abixy-het
-run_mlr fraction -f x,y -g a   -p -c $indir/abixy-het
-run_mlr fraction -f x,y -g a,b -p -c $indir/abixy-het
diff --git a/go/reg-test/cases/case-verb-fraction.sh b/go/reg-test/cases/case-verb-fraction.sh
new file mode 100644
index 000000000..12274bc43
--- /dev/null
+++ b/go/reg-test/cases/case-verb-fraction.sh
@@ -0,0 +1,15 @@
+run_mlr --oxtab fraction -f x,y              $indir/abixy-het
+run_mlr --oxtab fraction -f x,y -g a         $indir/abixy-het
+run_mlr --oxtab fraction -f x,y -g a,b       $indir/abixy-het
+
+run_mlr --oxtab fraction -f x,y        -p    $indir/abixy-het
+run_mlr --oxtab fraction -f x,y -g a   -p    $indir/abixy-het
+run_mlr --oxtab fraction -f x,y -g a,b -p    $indir/abixy-het
+
+run_mlr --oxtab fraction -f x,y           -c $indir/abixy-het
+run_mlr --oxtab fraction -f x,y -g a      -c $indir/abixy-het
+run_mlr --oxtab fraction -f x,y -g a,b    -c $indir/abixy-het
+
+run_mlr --oxtab fraction -f x,y        -p -c $indir/abixy-het
+run_mlr --oxtab fraction -f x,y -g a   -p -c $indir/abixy-het
+run_mlr --oxtab fraction -f x,y -g a,b -p -c $indir/abixy-het
diff --git a/go/reg-test/expected/case-c-verb-fraction.sh.out b/go/reg-test/expected/case-c-verb-fraction.sh.out
deleted file mode 100644
index e3367ae59..000000000
--- a/go/reg-test/expected/case-c-verb-fraction.sh.out
+++ /dev/null
@@ -1,145 +0,0 @@
-
-mlr fraction -f x,y ./reg-test/input/abixy-het
-a=pan,b=pan,i=1,x=0.3467901443380824,y=0.7268028627434533,x_fraction=0.087507,y_fraction=0.146286
-a=eks,b=pan,i=2,x=0.7586799647899636,y=0.5221511083334797,x_fraction=0.191441,y_fraction=0.105095
-aaa=wye,b=wye,i=3,x=0.20460330576630303,y=0.33831852551664776,x_fraction=0.051628,y_fraction=0.068095
-a=eks,bbb=wye,i=4,x=0.38139939387114097,y=0.13418874328430463,x_fraction=0.096240,y_fraction=0.027009
-a=wye,b=pan,i=5,xxx=0.5732889198020006,y=0.8636244699032729,y_fraction=0.173825
-a=zee,b=pan,i=6,x=0.5271261600918548,y=0.49322128674835697,x_fraction=0.133012,y_fraction=0.099272
-a=eks,b=zee,iii=7,x=0.6117840605678454,y=0.1878849191181694,x_fraction=0.154374,y_fraction=0.037816
-a=zee,b=wye,i=8,x=0.5985540091064224,yyy=0.976181385699006,x_fraction=0.151035
-aaa=hat,bbb=wye,i=9,x=0.03144187646093577,y=0.7495507603507059,x_fraction=0.007934,y_fraction=0.150865
-a=pan,b=wye,i=10,x=0.5026260055412137,y=0.9526183602969864,x_fraction=0.126830,y_fraction=0.191737
-
-mlr fraction -f x,y -g a ./reg-test/input/abixy-het
-a=pan,b=pan,i=1,x=0.3467901443380824,y=0.7268028627434533,x_fraction=0.408269,y_fraction=0.432770
-a=eks,b=pan,i=2,x=0.7586799647899636,y=0.5221511083334797,x_fraction=0.433070,y_fraction=0.618498
-aaa=wye,b=wye,i=3,x=0.20460330576630303,y=0.33831852551664776
-a=eks,bbb=wye,i=4,x=0.38139939387114097,y=0.13418874328430463,x_fraction=0.217711,y_fraction=0.158949
-a=wye,b=pan,i=5,xxx=0.5732889198020006,y=0.8636244699032729,y_fraction=1.000000
-a=zee,b=pan,i=6,x=0.5271261600918548,y=0.49322128674835697,x_fraction=0.468273,y_fraction=1.000000
-a=eks,b=zee,iii=7,x=0.6117840605678454,y=0.1878849191181694,x_fraction=0.349219,y_fraction=0.222553
-a=zee,b=wye,i=8,x=0.5985540091064224,yyy=0.976181385699006,x_fraction=0.531727
-aaa=hat,bbb=wye,i=9,x=0.03144187646093577,y=0.7495507603507059
-a=pan,b=wye,i=10,x=0.5026260055412137,y=0.9526183602969864,x_fraction=0.591731,y_fraction=0.567230
-
-mlr fraction -f x,y -g a,b ./reg-test/input/abixy-het
-a=pan,b=pan,i=1,x=0.3467901443380824,y=0.7268028627434533,x_fraction=1.000000,y_fraction=1.000000
-a=eks,b=pan,i=2,x=0.7586799647899636,y=0.5221511083334797,x_fraction=1.000000,y_fraction=1.000000
-aaa=wye,b=wye,i=3,x=0.20460330576630303,y=0.33831852551664776
-a=eks,bbb=wye,i=4,x=0.38139939387114097,y=0.13418874328430463
-a=wye,b=pan,i=5,xxx=0.5732889198020006,y=0.8636244699032729,y_fraction=1.000000
-a=zee,b=pan,i=6,x=0.5271261600918548,y=0.49322128674835697,x_fraction=1.000000,y_fraction=1.000000
-a=eks,b=zee,iii=7,x=0.6117840605678454,y=0.1878849191181694,x_fraction=1.000000,y_fraction=1.000000
-a=zee,b=wye,i=8,x=0.5985540091064224,yyy=0.976181385699006,x_fraction=1.000000
-aaa=hat,bbb=wye,i=9,x=0.03144187646093577,y=0.7495507603507059
-a=pan,b=wye,i=10,x=0.5026260055412137,y=0.9526183602969864,x_fraction=1.000000,y_fraction=1.000000
-
-mlr fraction -f x,y -p ./reg-test/input/abixy-het
-a=pan,b=pan,i=1,x=0.3467901443380824,y=0.7268028627434533,x_percent=8.750687,y_percent=14.628624
-a=eks,b=pan,i=2,x=0.7586799647899636,y=0.5221511083334797,x_percent=19.144058,y_percent=10.509524
-aaa=wye,b=wye,i=3,x=0.20460330576630303,y=0.33831852551664776,x_percent=5.162832,y_percent=6.809459
-a=eks,bbb=wye,i=4,x=0.38139939387114097,y=0.13418874328430463,x_percent=9.623995,y_percent=2.700865
-a=wye,b=pan,i=5,xxx=0.5732889198020006,y=0.8636244699032729,y_percent=17.382482
-a=zee,b=pan,i=6,x=0.5271261600918548,y=0.49322128674835697,x_percent=13.301173,y_percent=9.927243
-a=eks,b=zee,iii=7,x=0.6117840605678454,y=0.1878849191181694,x_percent=15.437378,y_percent=3.781628
-a=zee,b=wye,i=8,x=0.5985540091064224,yyy=0.976181385699006,x_percent=15.103539
-aaa=hat,bbb=wye,i=9,x=0.03144187646093577,y=0.7495507603507059,x_percent=0.793385,y_percent=15.086479
-a=pan,b=wye,i=10,x=0.5026260055412137,y=0.9526183602969864,x_percent=12.682952,y_percent=19.173694
-
-mlr fraction -f x,y -g a -p ./reg-test/input/abixy-het
-a=pan,b=pan,i=1,x=0.3467901443380824,y=0.7268028627434533,x_percent=40.826884,y_percent=43.276985
-a=eks,b=pan,i=2,x=0.7586799647899636,y=0.5221511083334797,x_percent=43.307027,y_percent=61.849773
-aaa=wye,b=wye,i=3,x=0.20460330576630303,y=0.33831852551664776
-a=eks,bbb=wye,i=4,x=0.38139939387114097,y=0.13418874328430463,x_percent=21.771069,y_percent=15.894907
-a=wye,b=pan,i=5,xxx=0.5732889198020006,y=0.8636244699032729,y_percent=100.000000
-a=zee,b=pan,i=6,x=0.5271261600918548,y=0.49322128674835697,x_percent=46.827347,y_percent=100.000000
-a=eks,b=zee,iii=7,x=0.6117840605678454,y=0.1878849191181694,x_percent=34.921904,y_percent=22.255319
-a=zee,b=wye,i=8,x=0.5985540091064224,yyy=0.976181385699006,x_percent=53.172653
-aaa=hat,bbb=wye,i=9,x=0.03144187646093577,y=0.7495507603507059
-a=pan,b=wye,i=10,x=0.5026260055412137,y=0.9526183602969864,x_percent=59.173116,y_percent=56.723015
-
-mlr fraction -f x,y -g a,b -p ./reg-test/input/abixy-het
-a=pan,b=pan,i=1,x=0.3467901443380824,y=0.7268028627434533,x_percent=100.000000,y_percent=100.000000
-a=eks,b=pan,i=2,x=0.7586799647899636,y=0.5221511083334797,x_percent=100.000000,y_percent=100.000000
-aaa=wye,b=wye,i=3,x=0.20460330576630303,y=0.33831852551664776
-a=eks,bbb=wye,i=4,x=0.38139939387114097,y=0.13418874328430463
-a=wye,b=pan,i=5,xxx=0.5732889198020006,y=0.8636244699032729,y_percent=100.000000
-a=zee,b=pan,i=6,x=0.5271261600918548,y=0.49322128674835697,x_percent=100.000000,y_percent=100.000000
-a=eks,b=zee,iii=7,x=0.6117840605678454,y=0.1878849191181694,x_percent=100.000000,y_percent=100.000000
-a=zee,b=wye,i=8,x=0.5985540091064224,yyy=0.976181385699006,x_percent=100.000000
-aaa=hat,bbb=wye,i=9,x=0.03144187646093577,y=0.7495507603507059
-a=pan,b=wye,i=10,x=0.5026260055412137,y=0.9526183602969864,x_percent=100.000000,y_percent=100.000000
-
-mlr fraction -f x,y -c ./reg-test/input/abixy-het
-a=pan,b=pan,i=1,x=0.3467901443380824,y=0.7268028627434533,x_cumulative_fraction=0.087507,y_cumulative_fraction=0.146286
-a=eks,b=pan,i=2,x=0.7586799647899636,y=0.5221511083334797,x_cumulative_fraction=0.278947,y_cumulative_fraction=0.251381
-aaa=wye,b=wye,i=3,x=0.20460330576630303,y=0.33831852551664776,x_cumulative_fraction=0.330576,y_cumulative_fraction=0.319476
-a=eks,bbb=wye,i=4,x=0.38139939387114097,y=0.13418874328430463,x_cumulative_fraction=0.426816,y_cumulative_fraction=0.346485
-a=wye,b=pan,i=5,xxx=0.5732889198020006,y=0.8636244699032729,y_cumulative_fraction=0.520310
-a=zee,b=pan,i=6,x=0.5271261600918548,y=0.49322128674835697,x_cumulative_fraction=0.559827,y_cumulative_fraction=0.619582
-a=eks,b=zee,iii=7,x=0.6117840605678454,y=0.1878849191181694,x_cumulative_fraction=0.714201,y_cumulative_fraction=0.657398
-a=zee,b=wye,i=8,x=0.5985540091064224,yyy=0.976181385699006,x_cumulative_fraction=0.865237
-aaa=hat,bbb=wye,i=9,x=0.03144187646093577,y=0.7495507603507059,x_cumulative_fraction=0.873170,y_cumulative_fraction=0.808263
-a=pan,b=wye,i=10,x=0.5026260055412137,y=0.9526183602969864,x_cumulative_fraction=1.000000,y_cumulative_fraction=1.000000
-
-mlr fraction -f x,y -g a -c ./reg-test/input/abixy-het
-a=pan,b=pan,i=1,x=0.3467901443380824,y=0.7268028627434533,x_cumulative_fraction=0.408269,y_cumulative_fraction=0.432770
-a=eks,b=pan,i=2,x=0.7586799647899636,y=0.5221511083334797,x_cumulative_fraction=0.433070,y_cumulative_fraction=0.618498
-aaa=wye,b=wye,i=3,x=0.20460330576630303,y=0.33831852551664776
-a=eks,bbb=wye,i=4,x=0.38139939387114097,y=0.13418874328430463,x_cumulative_fraction=0.650781,y_cumulative_fraction=0.777447
-a=wye,b=pan,i=5,xxx=0.5732889198020006,y=0.8636244699032729,y_cumulative_fraction=1.000000
-a=zee,b=pan,i=6,x=0.5271261600918548,y=0.49322128674835697,x_cumulative_fraction=0.468273,y_cumulative_fraction=1.000000
-a=eks,b=zee,iii=7,x=0.6117840605678454,y=0.1878849191181694,x_cumulative_fraction=1.000000,y_cumulative_fraction=1.000000
-a=zee,b=wye,i=8,x=0.5985540091064224,yyy=0.976181385699006,x_cumulative_fraction=1.000000
-aaa=hat,bbb=wye,i=9,x=0.03144187646093577,y=0.7495507603507059
-a=pan,b=wye,i=10,x=0.5026260055412137,y=0.9526183602969864,x_cumulative_fraction=1.000000,y_cumulative_fraction=1.000000
-
-mlr fraction -f x,y -g a,b -c ./reg-test/input/abixy-het
-a=pan,b=pan,i=1,x=0.3467901443380824,y=0.7268028627434533,x_cumulative_fraction=1.000000,y_cumulative_fraction=1.000000
-a=eks,b=pan,i=2,x=0.7586799647899636,y=0.5221511083334797,x_cumulative_fraction=1.000000,y_cumulative_fraction=1.000000
-aaa=wye,b=wye,i=3,x=0.20460330576630303,y=0.33831852551664776
-a=eks,bbb=wye,i=4,x=0.38139939387114097,y=0.13418874328430463
-a=wye,b=pan,i=5,xxx=0.5732889198020006,y=0.8636244699032729,y_cumulative_fraction=1.000000
-a=zee,b=pan,i=6,x=0.5271261600918548,y=0.49322128674835697,x_cumulative_fraction=1.000000,y_cumulative_fraction=1.000000
-a=eks,b=zee,iii=7,x=0.6117840605678454,y=0.1878849191181694,x_cumulative_fraction=1.000000,y_cumulative_fraction=1.000000
-a=zee,b=wye,i=8,x=0.5985540091064224,yyy=0.976181385699006,x_cumulative_fraction=1.000000
-aaa=hat,bbb=wye,i=9,x=0.03144187646093577,y=0.7495507603507059
-a=pan,b=wye,i=10,x=0.5026260055412137,y=0.9526183602969864,x_cumulative_fraction=1.000000,y_cumulative_fraction=1.000000
-
-mlr fraction -f x,y -p -c ./reg-test/input/abixy-het
-a=pan,b=pan,i=1,x=0.3467901443380824,y=0.7268028627434533,x_cumulative_percent=8.750687,y_cumulative_percent=14.628624
-a=eks,b=pan,i=2,x=0.7586799647899636,y=0.5221511083334797,x_cumulative_percent=27.894745,y_cumulative_percent=25.138148
-aaa=wye,b=wye,i=3,x=0.20460330576630303,y=0.33831852551664776,x_cumulative_percent=33.057577,y_cumulative_percent=31.947608
-a=eks,bbb=wye,i=4,x=0.38139939387114097,y=0.13418874328430463,x_cumulative_percent=42.681572,y_cumulative_percent=34.648473
-a=wye,b=pan,i=5,xxx=0.5732889198020006,y=0.8636244699032729,y_cumulative_percent=52.030955
-a=zee,b=pan,i=6,x=0.5271261600918548,y=0.49322128674835697,x_cumulative_percent=55.982746,y_cumulative_percent=61.958199
-a=eks,b=zee,iii=7,x=0.6117840605678454,y=0.1878849191181694,x_cumulative_percent=71.420124,y_cumulative_percent=65.739826
-a=zee,b=wye,i=8,x=0.5985540091064224,yyy=0.976181385699006,x_cumulative_percent=86.523663
-aaa=hat,bbb=wye,i=9,x=0.03144187646093577,y=0.7495507603507059,x_cumulative_percent=87.317048,y_cumulative_percent=80.826306
-a=pan,b=wye,i=10,x=0.5026260055412137,y=0.9526183602969864,x_cumulative_percent=100.000000,y_cumulative_percent=100.000000
-
-mlr fraction -f x,y -g a -p -c ./reg-test/input/abixy-het
-a=pan,b=pan,i=1,x=0.3467901443380824,y=0.7268028627434533,x_cumulative_percent=40.826884,y_cumulative_percent=43.276985
-a=eks,b=pan,i=2,x=0.7586799647899636,y=0.5221511083334797,x_cumulative_percent=43.307027,y_cumulative_percent=61.849773
-aaa=wye,b=wye,i=3,x=0.20460330576630303,y=0.33831852551664776
-a=eks,bbb=wye,i=4,x=0.38139939387114097,y=0.13418874328430463,x_cumulative_percent=65.078096,y_cumulative_percent=77.744681
-a=wye,b=pan,i=5,xxx=0.5732889198020006,y=0.8636244699032729,y_cumulative_percent=100.000000
-a=zee,b=pan,i=6,x=0.5271261600918548,y=0.49322128674835697,x_cumulative_percent=46.827347,y_cumulative_percent=100.000000
-a=eks,b=zee,iii=7,x=0.6117840605678454,y=0.1878849191181694,x_cumulative_percent=100.000000,y_cumulative_percent=100.000000
-a=zee,b=wye,i=8,x=0.5985540091064224,yyy=0.976181385699006,x_cumulative_percent=100.000000
-aaa=hat,bbb=wye,i=9,x=0.03144187646093577,y=0.7495507603507059
-a=pan,b=wye,i=10,x=0.5026260055412137,y=0.9526183602969864,x_cumulative_percent=100.000000,y_cumulative_percent=100.000000
-
-mlr fraction -f x,y -g a,b -p -c ./reg-test/input/abixy-het
-a=pan,b=pan,i=1,x=0.3467901443380824,y=0.7268028627434533,x_cumulative_percent=100.000000,y_cumulative_percent=100.000000
-a=eks,b=pan,i=2,x=0.7586799647899636,y=0.5221511083334797,x_cumulative_percent=100.000000,y_cumulative_percent=100.000000
-aaa=wye,b=wye,i=3,x=0.20460330576630303,y=0.33831852551664776
-a=eks,bbb=wye,i=4,x=0.38139939387114097,y=0.13418874328430463
-a=wye,b=pan,i=5,xxx=0.5732889198020006,y=0.8636244699032729,y_cumulative_percent=100.000000
-a=zee,b=pan,i=6,x=0.5271261600918548,y=0.49322128674835697,x_cumulative_percent=100.000000,y_cumulative_percent=100.000000
-a=eks,b=zee,iii=7,x=0.6117840605678454,y=0.1878849191181694,x_cumulative_percent=100.000000,y_cumulative_percent=100.000000
-a=zee,b=wye,i=8,x=0.5985540091064224,yyy=0.976181385699006,x_cumulative_percent=100.000000
-aaa=hat,bbb=wye,i=9,x=0.03144187646093577,y=0.7495507603507059
-a=pan,b=wye,i=10,x=0.5026260055412137,y=0.9526183602969864,x_cumulative_percent=100.000000,y_cumulative_percent=100.000000
-
diff --git a/go/reg-test/expected/case-cli-help.sh.out b/go/reg-test/expected/case-cli-help.sh.out
index 59d742668..cbce6e990 100644
--- a/go/reg-test/expected/case-cli-help.sh.out
+++ b/go/reg-test/expected/case-cli-help.sh.out
@@ -149,6 +149,27 @@ Options:
 -s Separator, defaulting to mlr --oflatsep value.
 -h|--help Show this message.
 ================================================================
+Usage: mlr fraction [options]
+For each record's value in specified fields, computes the ratio of that
+value to the sum of values in that field over all input records.
+E.g. with input records  x=1  x=2  x=3  and  x=4, emits output records
+x=1,x_fraction=0.1  x=2,x_fraction=0.2  x=3,x_fraction=0.3  and  x=4,x_fraction=0.4
+
+Note: this is internally a two-pass algorithm: on the first pass it retains
+input records and accumulates sums; on the second pass it computes quotients
+and emits output records. This means it produces no output until all input is read.
+
+Options:
+-f {a,b,c}    Field name(s) for fraction calculation
+-g {d,e,f}    Optional group-by-field name(s) for fraction counts
+-p            Produce percents [0..100], not fractions [0..1]. Output field names
+              end with "_percent" rather than "_fraction"
+-c            Produce cumulative distributions, i.e. running sums: each output
+              value folds in the sum of the previous for the specified group
+              E.g. with input records  x=1  x=2  x=3  and  x=4, emits output records
+              x=1,x_cumulative_fraction=0.1  x=2,x_cumulative_fraction=0.3
+              x=3,x_cumulative_fraction=0.6  and  x=4,x_cumulative_fraction=1.0
+================================================================
 Usage: mlr gap [options]
 Emits an empty record every n records, or when certain values change.
 Options:
@@ -218,6 +239,20 @@ Usage: mlr histogram [options]
 -o {prefix}   Prefix for output field name. Default: no prefix.
 -h|--help Show this message.
 ================================================================
+Usage: mlr json-parse [options]
+Tries to convert string field values to parsed JSON, e.g. "[1,2,3]" -> [1,2,3].
+Options:
+-f {...} Comma-separated list of field names to json-parse (default all).
+-h|--help Show this message.
+================================================================
+Usage: mlr json-stringify [options]
+Produces string field values from field-value data, e.g. [1,2,3] -> "[1,2,3]".
+Options:
+-f {...} Comma-separated list of field names to json-parse (default all).
+--jvstack Produce multi-line JSON output.
+--no-jvstack Produce single-line JSON output per record (default).
+-h|--help Show this message.
+================================================================
 Usage: mlr join [options]
 Joins records from specified left file name with records from all file names
 at the end of the Miller argument list.
@@ -261,20 +296,6 @@ Please use "mlr --usage-separator-options" for information on specifying separat
 Please see https://miller.readthedocs.io/en/latest/reference-verbs.html#join for more information
 including examples.
 ================================================================
-Usage: mlr json-parse [options]
-Tries to convert string field values to parsed JSON, e.g. "[1,2,3]" -> [1,2,3].
-Options:
--f {...} Comma-separated list of field names to json-parse (default all).
--h|--help Show this message.
-================================================================
-Usage: mlr json-stringify [options]
-Produces string field values from field-value data, e.g. [1,2,3] -> "[1,2,3]".
-Options:
--f {...} Comma-separated list of field names to json-parse (default all).
---jvstack Produce multi-line JSON output.
---no-jvstack Produce single-line JSON output per record (default).
--h|--help Show this message.
-================================================================
 Usage: mlr label [options] {new1,new2,new3,...}
 Given n comma-separated names, renames the first n fields of each record to
 have the respective name. (Fields past the nth are left with their original
@@ -330,32 +351,6 @@ semicolons to separate expressions.)
 
 -h|--help Show this message.
 ================================================================
-Usage: mlr repeat [options]
-Copies input records to output records multiple times.
-Options must be exactly one of the following:
--n {repeat count}  Repeat each input record this many times.
--f {field name}    Same, but take the repeat count from the specified
-                   field name of each input record.
--h|--help Show this message.
-Example:
-  echo x=0 | mlr repeat -n 4 then put '$x=urand()'
-produces:
- x=0.488189
- x=0.484973
- x=0.704983
- x=0.147311
-Example:
-  echo a=1,b=2,c=3 | mlr repeat -f b
-produces:
-  a=1,b=2,c=3
-  a=1,b=2,c=3
-Example:
-  echo a=1,b=2,c=3 | mlr repeat -f c
-produces:
-  a=1,b=2,c=3
-  a=1,b=2,c=3
-  a=1,b=2,c=3
-================================================================
 Usage: mlr regularize [options]
 Outputs records sorted lexically ascending by keys.Options:
 -h|--help Show this message.
@@ -398,6 +393,32 @@ Examples:
 mlr reorder    -f a,b sends input record "d=4,b=2,a=1,c=3" to "a=1,b=2,d=4,c=3".
 mlr reorder -e -f a,b sends input record "d=4,b=2,a=1,c=3" to "d=4,c=3,a=1,b=2".
 ================================================================
+Usage: mlr repeat [options]
+Copies input records to output records multiple times.
+Options must be exactly one of the following:
+-n {repeat count}  Repeat each input record this many times.
+-f {field name}    Same, but take the repeat count from the specified
+                   field name of each input record.
+-h|--help Show this message.
+Example:
+  echo x=0 | mlr repeat -n 4 then put '$x=urand()'
+produces:
+ x=0.488189
+ x=0.484973
+ x=0.704983
+ x=0.147311
+Example:
+  echo a=1,b=2,c=3 | mlr repeat -f b
+produces:
+  a=1,b=2,c=3
+  a=1,b=2,c=3
+Example:
+  echo a=1,b=2,c=3 | mlr repeat -f c
+produces:
+  a=1,b=2,c=3
+  a=1,b=2,c=3
+  a=1,b=2,c=3
+================================================================
 Usage: mlr sample [options]
 Reservoir sampling (subsampling without replacement), optionally by category.
 See also mlr bootstrap and mlr shuffle.
@@ -565,6 +586,13 @@ Prints records in reverse order from the order in which they were encountered.
 Options:
 -h|--help Show this message.
 ================================================================
+Usage: mlr tail [options]
+Passes through the last n records, optionally by category.
+Options:
+-g {a,b,c} Optional group-by-field names for head counts, e.g. a,b,c.
+-n {n} Head-count to print. Default 10.
+-h|--help Show this message.
+================================================================
 Usage: mlr tee [options] {filename}
 Options:
 -a    Append to existing file, if any, rather than overwriting.
@@ -574,13 +602,6 @@ Any of the output-format command-line flags (see mlr -h). Example: using
 the input is CSV, the output is pretty-print tabular, but the tee-file output
 is written in JSON format.
 
--h|--help Show this message.
-================================================================
-Usage: mlr tail [options]
-Passes through the last n records, optionally by category.
-Options:
--g {a,b,c} Optional group-by-field names for head counts, e.g. a,b,c.
--n {n} Head-count to print. Default 10.
 -h|--help Show this message.
 ================================================================
 Usage: mlr unflatten [options]
diff --git a/go/reg-test/expected/case-verb-fraction.sh.out b/go/reg-test/expected/case-verb-fraction.sh.out
new file mode 100644
index 000000000..b3b68f0ee
--- /dev/null
+++ b/go/reg-test/expected/case-verb-fraction.sh.out
@@ -0,0 +1,909 @@
+
+mlr --oxtab fraction -f x,y ./reg-test/input/abixy-het
+a          pan
+b          pan
+i          1
+x          0.3467901443380824
+y          0.7268028627434533
+x_fraction 0.08750686695876585
+y_fraction 0.1462862415661702
+
+a          eks
+b          pan
+i          2
+x          0.7586799647899636
+y          0.5221511083334797
+x_fraction 0.19144058107497372
+y_fraction 0.10509524257979809
+
+aaa        wye
+b          wye
+i          3
+x          0.20460330576630303
+y          0.33831852551664776
+x_fraction 0.051628324937518816
+y_fraction 0.06809459357827034
+
+a          eks
+bbb        wye
+i          4
+x          0.38139939387114097
+y          0.13418874328430463
+x_fraction 0.09623994961373192
+y_fraction 0.027008653820448102
+
+a          wye
+b          pan
+i          5
+xxx        0.5732889198020006
+y          0.8636244699032729
+y_fraction 0.17382482142385294
+
+a          zee
+b          pan
+i          6
+x          0.5271261600918548
+y          0.49322128674835697
+x_fraction 0.13301173494905932
+y_fraction 0.09927243272886704
+
+a          eks
+b          zee
+iii        7
+x          0.6117840605678454
+y          0.1878849191181694
+x_fraction 0.1543737827318787
+y_fraction 0.037816277389185964
+
+a          zee
+b          wye
+i          8
+x          0.5985540091064224
+yyy        0.976181385699006
+x_fraction 0.15103539387627238
+
+aaa        hat
+bbb        wye
+i          9
+x          0.03144187646093577
+y          0.7495507603507059
+x_fraction 0.00793384744440362
+y_fraction 0.15086479321349863
+
+a          pan
+b          wye
+i          10
+x          0.5026260055412137
+y          0.9526183602969864
+x_fraction 0.1268295184133955
+y_fraction 0.19173694369990862
+
+mlr --oxtab fraction -f x,y -g a ./reg-test/input/abixy-het
+a          pan
+b          pan
+i          1
+x          0.3467901443380824
+y          0.7268028627434533
+x_fraction 0.4082688378215578
+y_fraction 0.4327698452134853
+
+a          eks
+b          pan
+i          2
+x          0.7586799647899636
+y          0.5221511083334797
+x_fraction 0.4330702704688488
+y_fraction 0.6184977347659367
+
+aaa wye
+b   wye
+i   3
+x   0.20460330576630303
+y   0.33831852551664776
+
+a          eks
+bbb        wye
+i          4
+x          0.38139939387114097
+y          0.13418874328430463
+x_fraction 0.2177106900485466
+y_fraction 0.15894907130872915
+
+a          wye
+b          pan
+i          5
+xxx        0.5732889198020006
+y          0.8636244699032729
+y_fraction 1
+
+a          zee
+b          pan
+i          6
+x          0.5271261600918548
+y          0.49322128674835697
+x_fraction 0.46827347102266204
+y_fraction 1
+
+a          eks
+b          zee
+iii        7
+x          0.6117840605678454
+y          0.1878849191181694
+x_fraction 0.34921903948260463
+y_fraction 0.22255319392533407
+
+a          zee
+b          wye
+i          8
+x          0.5985540091064224
+yyy        0.976181385699006
+x_fraction 0.531726528977338
+
+aaa hat
+bbb wye
+i   9
+x   0.03144187646093577
+y   0.7495507603507059
+
+a          pan
+b          wye
+i          10
+x          0.5026260055412137
+y          0.9526183602969864
+x_fraction 0.5917311621784421
+y_fraction 0.5672301547865147
+
+mlr --oxtab fraction -f x,y -g a,b ./reg-test/input/abixy-het
+a          pan
+b          pan
+i          1
+x          0.3467901443380824
+y          0.7268028627434533
+x_fraction 1
+y_fraction 1
+
+a          eks
+b          pan
+i          2
+x          0.7586799647899636
+y          0.5221511083334797
+x_fraction 1
+y_fraction 1
+
+aaa wye
+b   wye
+i   3
+x   0.20460330576630303
+y   0.33831852551664776
+
+a   eks
+bbb wye
+i   4
+x   0.38139939387114097
+y   0.13418874328430463
+
+a          wye
+b          pan
+i          5
+xxx        0.5732889198020006
+y          0.8636244699032729
+y_fraction 1
+
+a          zee
+b          pan
+i          6
+x          0.5271261600918548
+y          0.49322128674835697
+x_fraction 1
+y_fraction 1
+
+a          eks
+b          zee
+iii        7
+x          0.6117840605678454
+y          0.1878849191181694
+x_fraction 1
+y_fraction 1
+
+a          zee
+b          wye
+i          8
+x          0.5985540091064224
+yyy        0.976181385699006
+x_fraction 1
+
+aaa hat
+bbb wye
+i   9
+x   0.03144187646093577
+y   0.7495507603507059
+
+a          pan
+b          wye
+i          10
+x          0.5026260055412137
+y          0.9526183602969864
+x_fraction 1
+y_fraction 1
+
+mlr --oxtab fraction -f x,y -p ./reg-test/input/abixy-het
+a         pan
+b         pan
+i         1
+x         0.3467901443380824
+y         0.7268028627434533
+x_percent 8.750686695876585
+y_percent 14.62862415661702
+
+a         eks
+b         pan
+i         2
+x         0.7586799647899636
+y         0.5221511083334797
+x_percent 19.144058107497372
+y_percent 10.509524257979809
+
+aaa       wye
+b         wye
+i         3
+x         0.20460330576630303
+y         0.33831852551664776
+x_percent 5.162832493751882
+y_percent 6.809459357827034
+
+a         eks
+bbb       wye
+i         4
+x         0.38139939387114097
+y         0.13418874328430463
+x_percent 9.623994961373192
+y_percent 2.7008653820448103
+
+a         wye
+b         pan
+i         5
+xxx       0.5732889198020006
+y         0.8636244699032729
+y_percent 17.382482142385296
+
+a         zee
+b         pan
+i         6
+x         0.5271261600918548
+y         0.49322128674835697
+x_percent 13.301173494905932
+y_percent 9.927243272886704
+
+a         eks
+b         zee
+iii       7
+x         0.6117840605678454
+y         0.1878849191181694
+x_percent 15.437378273187871
+y_percent 3.7816277389185964
+
+a         zee
+b         wye
+i         8
+x         0.5985540091064224
+yyy       0.976181385699006
+x_percent 15.103539387627238
+
+aaa       hat
+bbb       wye
+i         9
+x         0.03144187646093577
+y         0.7495507603507059
+x_percent 0.7933847444403621
+y_percent 15.086479321349863
+
+a         pan
+b         wye
+i         10
+x         0.5026260055412137
+y         0.9526183602969864
+x_percent 12.682951841339548
+y_percent 19.173694369990862
+
+mlr --oxtab fraction -f x,y -g a -p ./reg-test/input/abixy-het
+a         pan
+b         pan
+i         1
+x         0.3467901443380824
+y         0.7268028627434533
+x_percent 40.82688378215578
+y_percent 43.27698452134853
+
+a         eks
+b         pan
+i         2
+x         0.7586799647899636
+y         0.5221511083334797
+x_percent 43.307027046884876
+y_percent 61.849773476593676
+
+aaa wye
+b   wye
+i   3
+x   0.20460330576630303
+y   0.33831852551664776
+
+a         eks
+bbb       wye
+i         4
+x         0.38139939387114097
+y         0.13418874328430463
+x_percent 21.77106900485466
+y_percent 15.894907130872916
+
+a         wye
+b         pan
+i         5
+xxx       0.5732889198020006
+y         0.8636244699032729
+y_percent 100
+
+a         zee
+b         pan
+i         6
+x         0.5271261600918548
+y         0.49322128674835697
+x_percent 46.8273471022662
+y_percent 100
+
+a         eks
+b         zee
+iii       7
+x         0.6117840605678454
+y         0.1878849191181694
+x_percent 34.921903948260464
+y_percent 22.25531939253341
+
+a         zee
+b         wye
+i         8
+x         0.5985540091064224
+yyy       0.976181385699006
+x_percent 53.1726528977338
+
+aaa hat
+bbb wye
+i   9
+x   0.03144187646093577
+y   0.7495507603507059
+
+a         pan
+b         wye
+i         10
+x         0.5026260055412137
+y         0.9526183602969864
+x_percent 59.17311621784421
+y_percent 56.723015478651476
+
+mlr --oxtab fraction -f x,y -g a,b -p ./reg-test/input/abixy-het
+a         pan
+b         pan
+i         1
+x         0.3467901443380824
+y         0.7268028627434533
+x_percent 100
+y_percent 100
+
+a         eks
+b         pan
+i         2
+x         0.7586799647899636
+y         0.5221511083334797
+x_percent 100
+y_percent 100
+
+aaa wye
+b   wye
+i   3
+x   0.20460330576630303
+y   0.33831852551664776
+
+a   eks
+bbb wye
+i   4
+x   0.38139939387114097
+y   0.13418874328430463
+
+a         wye
+b         pan
+i         5
+xxx       0.5732889198020006
+y         0.8636244699032729
+y_percent 100
+
+a         zee
+b         pan
+i         6
+x         0.5271261600918548
+y         0.49322128674835697
+x_percent 100
+y_percent 100
+
+a         eks
+b         zee
+iii       7
+x         0.6117840605678454
+y         0.1878849191181694
+x_percent 100
+y_percent 100
+
+a         zee
+b         wye
+i         8
+x         0.5985540091064224
+yyy       0.976181385699006
+x_percent 100
+
+aaa hat
+bbb wye
+i   9
+x   0.03144187646093577
+y   0.7495507603507059
+
+a         pan
+b         wye
+i         10
+x         0.5026260055412137
+y         0.9526183602969864
+x_percent 100
+y_percent 100
+
+mlr --oxtab fraction -f x,y -c ./reg-test/input/abixy-het
+a                     pan
+b                     pan
+i                     1
+x                     0.3467901443380824
+y                     0.7268028627434533
+x_cumulative_fraction 0.08750686695876585
+y_cumulative_fraction 0.1462862415661702
+
+a                     eks
+b                     pan
+i                     2
+x                     0.7586799647899636
+y                     0.5221511083334797
+x_cumulative_fraction 0.2789474480337396
+y_cumulative_fraction 0.2513814841459683
+
+aaa                   wye
+b                     wye
+i                     3
+x                     0.20460330576630303
+y                     0.33831852551664776
+x_cumulative_fraction 0.3305757729712584
+y_cumulative_fraction 0.3194760777242386
+
+a                     eks
+bbb                   wye
+i                     4
+x                     0.38139939387114097
+y                     0.13418874328430463
+x_cumulative_fraction 0.42681572258499034
+y_cumulative_fraction 0.34648473154468673
+
+a                     wye
+b                     pan
+i                     5
+xxx                   0.5732889198020006
+y                     0.8636244699032729
+y_cumulative_fraction 0.5203095529685396
+
+a                     zee
+b                     pan
+i                     6
+x                     0.5271261600918548
+y                     0.49322128674835697
+x_cumulative_fraction 0.5598274575340497
+y_cumulative_fraction 0.6195819856974067
+
+a                     eks
+b                     zee
+iii                   7
+x                     0.6117840605678454
+y                     0.1878849191181694
+x_cumulative_fraction 0.7142012402659285
+y_cumulative_fraction 0.6573982630865928
+
+a                     zee
+b                     wye
+i                     8
+x                     0.5985540091064224
+yyy                   0.976181385699006
+x_cumulative_fraction 0.8652366341422009
+
+aaa                   hat
+bbb                   wye
+i                     9
+x                     0.03144187646093577
+y                     0.7495507603507059
+x_cumulative_fraction 0.8731704815866045
+y_cumulative_fraction 0.8082630563000914
+
+a                     pan
+b                     wye
+i                     10
+x                     0.5026260055412137
+y                     0.9526183602969864
+x_cumulative_fraction 1
+y_cumulative_fraction 1
+
+mlr --oxtab fraction -f x,y -g a -c ./reg-test/input/abixy-het
+a                     pan
+b                     pan
+i                     1
+x                     0.3467901443380824
+y                     0.7268028627434533
+x_cumulative_fraction 0.4082688378215578
+y_cumulative_fraction 0.4327698452134853
+
+a                     eks
+b                     pan
+i                     2
+x                     0.7586799647899636
+y                     0.5221511083334797
+x_cumulative_fraction 0.4330702704688488
+y_cumulative_fraction 0.6184977347659367
+
+aaa wye
+b   wye
+i   3
+x   0.20460330576630303
+y   0.33831852551664776
+
+a                     eks
+bbb                   wye
+i                     4
+x                     0.38139939387114097
+y                     0.13418874328430463
+x_cumulative_fraction 0.6507809605173953
+y_cumulative_fraction 0.7774468060746659
+
+a                     wye
+b                     pan
+i                     5
+xxx                   0.5732889198020006
+y                     0.8636244699032729
+y_cumulative_fraction 1
+
+a                     zee
+b                     pan
+i                     6
+x                     0.5271261600918548
+y                     0.49322128674835697
+x_cumulative_fraction 0.46827347102266204
+y_cumulative_fraction 1
+
+a                     eks
+b                     zee
+iii                   7
+x                     0.6117840605678454
+y                     0.1878849191181694
+x_cumulative_fraction 1
+y_cumulative_fraction 1
+
+a                     zee
+b                     wye
+i                     8
+x                     0.5985540091064224
+yyy                   0.976181385699006
+x_cumulative_fraction 1
+
+aaa hat
+bbb wye
+i   9
+x   0.03144187646093577
+y   0.7495507603507059
+
+a                     pan
+b                     wye
+i                     10
+x                     0.5026260055412137
+y                     0.9526183602969864
+x_cumulative_fraction 1
+y_cumulative_fraction 1
+
+mlr --oxtab fraction -f x,y -g a,b -c ./reg-test/input/abixy-het
+a                     pan
+b                     pan
+i                     1
+x                     0.3467901443380824
+y                     0.7268028627434533
+x_cumulative_fraction 1
+y_cumulative_fraction 1
+
+a                     eks
+b                     pan
+i                     2
+x                     0.7586799647899636
+y                     0.5221511083334797
+x_cumulative_fraction 1
+y_cumulative_fraction 1
+
+aaa wye
+b   wye
+i   3
+x   0.20460330576630303
+y   0.33831852551664776
+
+a   eks
+bbb wye
+i   4
+x   0.38139939387114097
+y   0.13418874328430463
+
+a                     wye
+b                     pan
+i                     5
+xxx                   0.5732889198020006
+y                     0.8636244699032729
+y_cumulative_fraction 1
+
+a                     zee
+b                     pan
+i                     6
+x                     0.5271261600918548
+y                     0.49322128674835697
+x_cumulative_fraction 1
+y_cumulative_fraction 1
+
+a                     eks
+b                     zee
+iii                   7
+x                     0.6117840605678454
+y                     0.1878849191181694
+x_cumulative_fraction 1
+y_cumulative_fraction 1
+
+a                     zee
+b                     wye
+i                     8
+x                     0.5985540091064224
+yyy                   0.976181385699006
+x_cumulative_fraction 1
+
+aaa hat
+bbb wye
+i   9
+x   0.03144187646093577
+y   0.7495507603507059
+
+a                     pan
+b                     wye
+i                     10
+x                     0.5026260055412137
+y                     0.9526183602969864
+x_cumulative_fraction 1
+y_cumulative_fraction 1
+
+mlr --oxtab fraction -f x,y -p -c ./reg-test/input/abixy-het
+a                    pan
+b                    pan
+i                    1
+x                    0.3467901443380824
+y                    0.7268028627434533
+x_cumulative_percent 8.750686695876585
+y_cumulative_percent 14.62862415661702
+
+a                    eks
+b                    pan
+i                    2
+x                    0.7586799647899636
+y                    0.5221511083334797
+x_cumulative_percent 27.89474480337396
+y_cumulative_percent 25.138148414596827
+
+aaa                  wye
+b                    wye
+i                    3
+x                    0.20460330576630303
+y                    0.33831852551664776
+x_cumulative_percent 33.05757729712584
+y_cumulative_percent 31.947607772423858
+
+a                    eks
+bbb                  wye
+i                    4
+x                    0.38139939387114097
+y                    0.13418874328430463
+x_cumulative_percent 42.68157225849903
+y_cumulative_percent 34.648473154468675
+
+a                    wye
+b                    pan
+i                    5
+xxx                  0.5732889198020006
+y                    0.8636244699032729
+y_cumulative_percent 52.03095529685397
+
+a                    zee
+b                    pan
+i                    6
+x                    0.5271261600918548
+y                    0.49322128674835697
+x_cumulative_percent 55.98274575340497
+y_cumulative_percent 61.958198569740674
+
+a                    eks
+b                    zee
+iii                  7
+x                    0.6117840605678454
+y                    0.1878849191181694
+x_cumulative_percent 71.42012402659284
+y_cumulative_percent 65.73982630865927
+
+a                    zee
+b                    wye
+i                    8
+x                    0.5985540091064224
+yyy                  0.976181385699006
+x_cumulative_percent 86.52366341422008
+
+aaa                  hat
+bbb                  wye
+i                    9
+x                    0.03144187646093577
+y                    0.7495507603507059
+x_cumulative_percent 87.31704815866046
+y_cumulative_percent 80.82630563000914
+
+a                    pan
+b                    wye
+i                    10
+x                    0.5026260055412137
+y                    0.9526183602969864
+x_cumulative_percent 100
+y_cumulative_percent 100
+
+mlr --oxtab fraction -f x,y -g a -p -c ./reg-test/input/abixy-het
+a                    pan
+b                    pan
+i                    1
+x                    0.3467901443380824
+y                    0.7268028627434533
+x_cumulative_percent 40.82688378215578
+y_cumulative_percent 43.27698452134853
+
+a                    eks
+b                    pan
+i                    2
+x                    0.7586799647899636
+y                    0.5221511083334797
+x_cumulative_percent 43.307027046884876
+y_cumulative_percent 61.849773476593676
+
+aaa wye
+b   wye
+i   3
+x   0.20460330576630303
+y   0.33831852551664776
+
+a                    eks
+bbb                  wye
+i                    4
+x                    0.38139939387114097
+y                    0.13418874328430463
+x_cumulative_percent 65.07809605173954
+y_cumulative_percent 77.74468060746659
+
+a                    wye
+b                    pan
+i                    5
+xxx                  0.5732889198020006
+y                    0.8636244699032729
+y_cumulative_percent 100
+
+a                    zee
+b                    pan
+i                    6
+x                    0.5271261600918548
+y                    0.49322128674835697
+x_cumulative_percent 46.8273471022662
+y_cumulative_percent 100
+
+a                    eks
+b                    zee
+iii                  7
+x                    0.6117840605678454
+y                    0.1878849191181694
+x_cumulative_percent 100
+y_cumulative_percent 100
+
+a                    zee
+b                    wye
+i                    8
+x                    0.5985540091064224
+yyy                  0.976181385699006
+x_cumulative_percent 100
+
+aaa hat
+bbb wye
+i   9
+x   0.03144187646093577
+y   0.7495507603507059
+
+a                    pan
+b                    wye
+i                    10
+x                    0.5026260055412137
+y                    0.9526183602969864
+x_cumulative_percent 100
+y_cumulative_percent 100
+
+mlr --oxtab fraction -f x,y -g a,b -p -c ./reg-test/input/abixy-het
+a                    pan
+b                    pan
+i                    1
+x                    0.3467901443380824
+y                    0.7268028627434533
+x_cumulative_percent 100
+y_cumulative_percent 100
+
+a                    eks
+b                    pan
+i                    2
+x                    0.7586799647899636
+y                    0.5221511083334797
+x_cumulative_percent 100
+y_cumulative_percent 100
+
+aaa wye
+b   wye
+i   3
+x   0.20460330576630303
+y   0.33831852551664776
+
+a   eks
+bbb wye
+i   4
+x   0.38139939387114097
+y   0.13418874328430463
+
+a                    wye
+b                    pan
+i                    5
+xxx                  0.5732889198020006
+y                    0.8636244699032729
+y_cumulative_percent 100
+
+a                    zee
+b                    pan
+i                    6
+x                    0.5271261600918548
+y                    0.49322128674835697
+x_cumulative_percent 100
+y_cumulative_percent 100
+
+a                    eks
+b                    zee
+iii                  7
+x                    0.6117840605678454
+y                    0.1878849191181694
+x_cumulative_percent 100
+y_cumulative_percent 100
+
+a                    zee
+b                    wye
+i                    8
+x                    0.5985540091064224
+yyy                  0.976181385699006
+x_cumulative_percent 100
+
+aaa hat
+bbb wye
+i   9
+x   0.03144187646093577
+y   0.7495507603507059
+
+a                    pan
+b                    wye
+i                    10
+x                    0.5026260055412137
+y                    0.9526183602969864
+x_cumulative_percent 100
+y_cumulative_percent 100
+
diff --git a/go/src/cli/mlrcli_transformers.go b/go/src/cli/mlrcli_transformers.go
index 0637e0a31..6dfdfc264 100644
--- a/go/src/cli/mlrcli_transformers.go
+++ b/go/src/cli/mlrcli_transformers.go
@@ -23,6 +23,7 @@ var MAPPER_LOOKUP_TABLE = []transforming.TransformerSetup{
 	transformers.FillDownSetup,
 	transformers.FilterSetup,
 	transformers.FlattenSetup,
+	transformers.FractionSetup,
 	transformers.GapSetup,
 	transformers.GrepSetup,
 	transformers.GroupBySetup,
@@ -30,17 +31,17 @@ var MAPPER_LOOKUP_TABLE = []transforming.TransformerSetup{
 	transformers.HavingFieldsSetup,
 	transformers.HeadSetup,
 	transformers.HistogramSetup,
-	transformers.JoinSetup,
 	transformers.JSONParseSetup,
 	transformers.JSONStringifySetup,
+	transformers.JoinSetup,
 	transformers.LabelSetup,
 	transformers.NothingSetup,
 	transformers.PutSetup,
-	transformers.RepeatSetup,
 	transformers.RegularizeSetup,
 	transformers.RemoveEmptyColumnsSetup,
 	transformers.RenameSetup,
 	transformers.ReorderSetup,
+	transformers.RepeatSetup,
 	transformers.SampleSetup,
 	transformers.Sec2GMTSetup,
 	transformers.SeqgenSetup,
@@ -51,8 +52,8 @@ var MAPPER_LOOKUP_TABLE = []transforming.TransformerSetup{
 	transformers.Stats1Setup,
 	transformers.StepSetup,
 	transformers.TacSetup,
-	transformers.TeeSetup,
 	transformers.TailSetup,
+	transformers.TeeSetup,
 	transformers.UnflattenSetup,
 	transformers.UnsparsifySetup,
 }
diff --git a/go/src/transformers/fraction.go b/go/src/transformers/fraction.go
new file mode 100644
index 000000000..16ec23c40
--- /dev/null
+++ b/go/src/transformers/fraction.go
@@ -0,0 +1,278 @@
+package transformers
+
+import (
+	"container/list"
+	"fmt"
+	"os"
+	"strings"
+
+	"miller/src/cliutil"
+	"miller/src/lib"
+	"miller/src/transforming"
+	"miller/src/types"
+)
+
+// ----------------------------------------------------------------
+const verbNameFraction = "fraction"
+
+var FractionSetup = transforming.TransformerSetup{
+	Verb:         verbNameFraction,
+	UsageFunc:    transformerFractionUsage,
+	ParseCLIFunc: transformerFractionParseCLI,
+	IgnoresInput: false,
+}
+
+func transformerFractionUsage(
+	o *os.File,
+	doExit bool,
+	exitCode int,
+) {
+	argv0 := lib.MlrExeName()
+	verb := verbNameFraction
+	fmt.Fprintf(o, "Usage: %s %s [options]\n", argv0, verb)
+	fmt.Fprintf(o, "For each record's value in specified fields, computes the ratio of that\n")
+	fmt.Fprintf(o, "value to the sum of values in that field over all input records.\n")
+	fmt.Fprintf(o, "E.g. with input records  x=1  x=2  x=3  and  x=4, emits output records\n")
+	fmt.Fprintf(o, "x=1,x_fraction=0.1  x=2,x_fraction=0.2  x=3,x_fraction=0.3  and  x=4,x_fraction=0.4\n")
+	fmt.Fprintf(o, "\n")
+	fmt.Fprintf(o, "Note: this is internally a two-pass algorithm: on the first pass it retains\n")
+	fmt.Fprintf(o, "input records and accumulates sums; on the second pass it computes quotients\n")
+	fmt.Fprintf(o, "and emits output records. This means it produces no output until all input is read.\n")
+	fmt.Fprintf(o, "\n")
+	fmt.Fprintf(o, "Options:\n")
+	fmt.Fprintf(o, "-f {a,b,c}    Field name(s) for fraction calculation\n")
+	fmt.Fprintf(o, "-g {d,e,f}    Optional group-by-field name(s) for fraction counts\n")
+	fmt.Fprintf(o, "-p            Produce percents [0..100], not fractions [0..1]. Output field names\n")
+	fmt.Fprintf(o, "              end with \"_percent\" rather than \"_fraction\"\n")
+	fmt.Fprintf(o, "-c            Produce cumulative distributions, i.e. running sums: each output\n")
+	fmt.Fprintf(o, "              value folds in the sum of the previous for the specified group\n")
+	fmt.Fprintf(o, "              E.g. with input records  x=1  x=2  x=3  and  x=4, emits output records\n")
+	fmt.Fprintf(o, "              x=1,x_cumulative_fraction=0.1  x=2,x_cumulative_fraction=0.3\n")
+	fmt.Fprintf(o, "              x=3,x_cumulative_fraction=0.6  and  x=4,x_cumulative_fraction=1.0\n")
+
+	if doExit {
+		os.Exit(exitCode)
+	}
+}
+
+func transformerFractionParseCLI(
+	pargi *int,
+	argc int,
+	args []string,
+	_ *cliutil.TReaderOptions,
+	__ *cliutil.TWriterOptions,
+) transforming.IRecordTransformer {
+
+	// Skip the verb name from the current spot in the mlr command line
+	argi := *pargi
+	verb := args[argi]
+	argi++
+
+	// Parse local flags
+	var fractionFieldNames []string = nil
+	var groupByFieldNames []string = nil
+	doPercents := false
+	doCumu := false
+
+	for argi < argc /* variable increment: 1 or 2 depending on flag */ {
+		opt := args[argi]
+		if !strings.HasPrefix(opt, "-") {
+			break // No more flag options to process
+		}
+		argi++
+
+		if opt == "-h" || opt == "--help" {
+			transformerFractionUsage(os.Stdout, true, 0)
+
+		} else if opt == "-f" {
+			fractionFieldNames = cliutil.VerbGetStringArrayArgOrDie(verb, opt, args, &argi, argc)
+
+		} else if opt == "-g" {
+			groupByFieldNames = cliutil.VerbGetStringArrayArgOrDie(verb, opt, args, &argi, argc)
+
+		} else if opt == "-p" {
+			doPercents = true
+
+		} else if opt == "-c" {
+			doCumu = true
+
+		} else {
+			transformerFractionUsage(os.Stderr, true, 1)
+		}
+	}
+
+	if fractionFieldNames == nil {
+		transformerFractionUsage(os.Stderr, true, 1)
+	}
+
+	transformer, _ := NewTransformerFraction(
+		fractionFieldNames,
+		groupByFieldNames,
+		doPercents,
+		doCumu,
+	)
+
+	*pargi = argi
+	return transformer
+}
+
+// ----------------------------------------------------------------
+type TransformerFraction struct {
+	fractionFieldNames []string
+	groupByFieldNames  []string
+	doCumu             bool
+
+	recordsAndContexts *list.List
+	// Two-level map: Group-by field names are the first keyset;
+	// fraction field names are keys into the second.
+	sums  map[string]map[string]*types.Mlrval
+	cumus map[string]map[string]*types.Mlrval
+
+	outputFieldNameSuffix string        // "_fraction" or "_percent"
+	multiplier            *types.Mlrval // 1.0 for fraction or 100.0 for percent
+	zero                  *types.Mlrval
+}
+
+// ----------------------------------------------------------------
+func NewTransformerFraction(
+	fractionFieldNames []string,
+	groupByFieldNames []string,
+	doPercents bool,
+	doCumu bool,
+) (*TransformerFraction, error) {
+
+	recordsAndContexts := list.New()
+	sums := make(map[string]map[string]*types.Mlrval)
+	cumus := make(map[string]map[string]*types.Mlrval)
+
+	var multiplier *types.Mlrval
+	var outputFieldNameSuffix string
+	if doPercents {
+		multiplier = types.MlrvalPointerFromInt(100)
+		if doCumu {
+			outputFieldNameSuffix = "_cumulative_percent"
+		} else {
+			outputFieldNameSuffix = "_percent"
+		}
+	} else {
+		multiplier = types.MlrvalPointerFromInt(1)
+		if doCumu {
+			outputFieldNameSuffix = "_cumulative_fraction"
+		} else {
+			outputFieldNameSuffix = "_fraction"
+		}
+	}
+
+	zero := types.MlrvalPointerFromInt(0)
+
+	return &TransformerFraction{
+		fractionFieldNames:    fractionFieldNames,
+		groupByFieldNames:     groupByFieldNames,
+		doCumu:                doCumu,
+		recordsAndContexts:    recordsAndContexts,
+		sums:                  sums,
+		cumus:                 cumus,
+		outputFieldNameSuffix: outputFieldNameSuffix,
+		multiplier:            multiplier,
+		zero:                  zero,
+	}, nil
+}
+
+// ----------------------------------------------------------------
+func (this *TransformerFraction) Transform(
+	inrecAndContext *types.RecordAndContext,
+	outputChannel chan<- *types.RecordAndContext,
+) {
+	if !inrecAndContext.EndOfStream { // Not end of stream; pass 1
+		inrec := inrecAndContext.Record
+
+		// Append records into a single output list (so that this verb is order-preserving).
+		this.recordsAndContexts.PushBack(inrecAndContext)
+
+		// Accumulate sums of fraction-field values grouped by group-by field names
+		groupingKey, hasAll := inrec.GetSelectedValuesJoined(this.groupByFieldNames)
+
+		if hasAll {
+			sumsForGroup := this.sums[groupingKey]
+			var cumusForGroup map[string]*types.Mlrval = nil
+			if sumsForGroup == nil {
+				sumsForGroup = make(map[string]*types.Mlrval)
+				this.sums[groupingKey] = sumsForGroup
+				cumusForGroup = make(map[string]*types.Mlrval)
+				this.cumus[groupingKey] = cumusForGroup
+			}
+			for _, fractionFieldName := range this.fractionFieldNames {
+				value := inrec.Get(fractionFieldName)
+				if value != nil {
+					value.AssertNumeric() // may fatal the process
+					sum := sumsForGroup[fractionFieldName]
+					if sum == nil { // First value for group
+						sumsForGroup[fractionFieldName] = value.Copy()
+						cumusForGroup[fractionFieldName] = this.zero
+					} else {
+						sumsForGroup[fractionFieldName] = types.MlrvalBinaryPlus(sum, value)
+					}
+				}
+			}
+		}
+
+	} else { // End of stream; pass 2
+		// Iterate over the retained records, decorating them with fraction fields.
+		endOfStreamContext := inrecAndContext.Context
+
+		for {
+			element := this.recordsAndContexts.Front()
+			if element == nil {
+				break
+			}
+			this.recordsAndContexts.Remove(element)
+			recordAndContext := element.Value.(*types.RecordAndContext)
+			outrec := recordAndContext.Record
+
+			groupingKey, hasAll := outrec.GetSelectedValuesJoined(this.groupByFieldNames)
+			if hasAll {
+				sumsForGroup := this.sums[groupingKey]
+				cumusForGroup := this.cumus[groupingKey]
+				lib.InternalCodingErrorIf(sumsForGroup == nil) // should have been populated on pass 1
+
+				for _, fractionFieldName := range this.fractionFieldNames {
+					value := outrec.Get(fractionFieldName)
+					if value != nil {
+						value.AssertNumeric() // may fatal the process
+
+						var numerator *types.Mlrval = nil
+						var cumu *types.Mlrval = nil
+						var outputValue *types.Mlrval = nil
+
+						if this.doCumu {
+							cumu = cumusForGroup[fractionFieldName]
+							numerator = types.MlrvalBinaryPlus(value, cumu)
+						} else {
+							numerator = value
+						}
+
+						denominator := sumsForGroup[fractionFieldName]
+						if !types.MlrvalEqualsAsBool(value, this.zero) {
+							outputValue = types.MlrvalDivide(numerator, denominator)
+							outputValue = types.MlrvalTimes(outputValue, this.multiplier)
+						} else {
+							outputValue = types.MLRVAL_ERROR
+						}
+
+						outrec.PutCopy(
+							fractionFieldName+this.outputFieldNameSuffix,
+							outputValue,
+						)
+
+						if this.doCumu {
+							cumusForGroup[fractionFieldName] = types.MlrvalBinaryPlus(cumu, value)
+						}
+					}
+				}
+			}
+
+			outputChannel <- types.NewRecordAndContext(outrec, &endOfStreamContext)
+		}
+		outputChannel <- inrecAndContext // end-of-stream marker
+	}
+}
diff --git a/go/src/types/mlrval_accessors.go b/go/src/types/mlrval_accessors.go
index 18839faa2..1a8561679 100644
--- a/go/src/types/mlrval_accessors.go
+++ b/go/src/types/mlrval_accessors.go
@@ -147,6 +147,10 @@ func (this *Mlrval) GetNumericToFloatValueOrDie() (floatValue float64) {
 	return floatValue
 }
 
+func (this *Mlrval) AssertNumeric() {
+	_ = this.GetNumericToFloatValueOrDie()
+}
+
 func (this *Mlrval) GetBoolValue() (boolValue bool, isBool bool) {
 	if this.mvtype == MT_BOOL {
 		return this.boolval, true
diff --git a/go/src/types/mlrval_functions_booleans.go b/go/src/types/mlrval_functions_booleans.go
index 7589fa38c..279537ae8 100644
--- a/go/src/types/mlrval_functions_booleans.go
+++ b/go/src/types/mlrval_functions_booleans.go
@@ -224,7 +224,6 @@ var eq_dispositions = [MT_DIM][MT_DIM]BinaryFunc{}
 
 func init() {
 	eq_dispositions = [MT_DIM][MT_DIM]BinaryFunc{
-
 		//       .  ERROR   ABSENT VOID     STRING   INT      FLOAT    BOOL   ARRAY    MAP
 		/*ERROR  */ {_erro, _erro, _erro, _erro, _erro, _erro, _erro, _erro, _erro},
 		/*ABSENT */ {_erro, _absn, _absn, _absn, _absn, _absn, _absn, _absn, _absn},
@@ -236,7 +235,6 @@ func init() {
 		/*ARRAY  */ {_erro, _absn, _fals, _fals, _fals, _fals, _fals, eq_b_aa, _fals},
 		/*MAP    */ {_erro, _absn, _fals, _fals, _fals, _fals, _fals, _fals, eq_b_mm},
 	}
-
 }
 
 var ne_dispositions = [MT_DIM][MT_DIM]BinaryFunc{
@@ -333,6 +331,14 @@ func MlrvalLessThanForSort(input1, input2 *Mlrval) bool {
 	return retval
 }
 
+// Convenience wrapper for non-DSL callsites that just want a bool
+func MlrvalEqualsAsBool(input1, input2 *Mlrval) bool {
+	mretval := eq_dispositions[input1.mvtype][input2.mvtype](input1, input2)
+	retval, ok := mretval.GetBoolValue()
+	lib.InternalCodingErrorIf(!ok)
+	return retval
+}
+
 // ----------------------------------------------------------------
 func MlrvalLogicalAND(input1, input2 *Mlrval) *Mlrval {
 	if input1.mvtype == MT_BOOL && input2.mvtype == MT_BOOL {
diff --git a/go/todo.txt b/go/todo.txt
index d73f3aca3..2d7282a5f 100644
--- a/go/todo.txt
+++ b/go/todo.txt
@@ -523,3 +523,4 @@ i https://en.wikipedia.org/wiki/Delimiter#Delimiter_collision
 * more copy-on-retain for concurrent pointer-mods
   o make a thorough audit, and warn everywhere
   o either do copy for all retainers, or treat inrecs as immutable ...
+  o 'this.recordsAndContexts.PushBack(inrecAndContext)' idiom needs copy everywhere ...