Miller in 10 minutes¶
Obtaining Miller¶
You can install Miller for various platforms as follows:
Linux:
yum install millerorapt-get install millerdepending on your flavor of LinuxMacOS:
brew install millerorport install millerdepending on your preference of Homebrew or MacPorts.Windows:
choco install millerusing Chocolatey.You can get latest builds for Linux, MacOS, and Windows by visiting https://github.com/johnkerl/miller/actions, selecting the latest build, and clicking _Artifacts_. (These are retained for 5 days after each commit.)
See also Building from source if you prefer – in particular, if your platform’s package manager doesn’t have the latest release.
As a first check, you should be able to run mlr --version at your system’s command prompt and see something like the following:
mlr --version
Miller v6.0.0-dev
As a second check, given (example.csv) you should be able to do
mlr --csv cat example.csv
color,shape,flag,index,quantity,rate
yellow,triangle,true,11,43.6498,9.8870
red,square,true,15,79.2778,0.0130
red,circle,true,16,13.8103,2.9010
red,square,false,48,77.5542,7.4670
purple,triangle,false,51,81.2290,8.5910
red,square,false,64,77.1991,9.5310
purple,triangle,false,65,80.1405,5.8240
yellow,circle,true,73,63.9785,4.2370
yellow,circle,true,87,63.5058,8.3350
purple,square,false,91,72.3735,8.2430
mlr --icsv --opprint cat example.csv
color shape flag index quantity rate
yellow triangle true 11 43.6498 9.8870
red square true 15 79.2778 0.0130
red circle true 16 13.8103 2.9010
red square false 48 77.5542 7.4670
purple triangle false 51 81.2290 8.5910
red square false 64 77.1991 9.5310
purple triangle false 65 80.1405 5.8240
yellow circle true 73 63.9785 4.2370
yellow circle true 87 63.5058 8.3350
purple square false 91 72.3735 8.2430
If you run into issues on these checks, please check out the resources on the Community page for help.
Miller verbs¶
Let’s take a quick look at some of the most useful Miller verbs – file-format-aware, name-index-empowered equivalents of standard system commands.
mlr cat is like system cat (or type on Windows) – it passes the data through unmodified:
mlr --csv cat example.csv
color,shape,flag,index,quantity,rate
yellow,triangle,true,11,43.6498,9.8870
red,square,true,15,79.2778,0.0130
red,circle,true,16,13.8103,2.9010
red,square,false,48,77.5542,7.4670
purple,triangle,false,51,81.2290,8.5910
red,square,false,64,77.1991,9.5310
purple,triangle,false,65,80.1405,5.8240
yellow,circle,true,73,63.9785,4.2370
yellow,circle,true,87,63.5058,8.3350
purple,square,false,91,72.3735,8.2430
But mlr cat can also do format conversion – for example, you can pretty-print in tabular format:
mlr --icsv --opprint cat example.csv
color shape flag index quantity rate
yellow triangle true 11 43.6498 9.8870
red square true 15 79.2778 0.0130
red circle true 16 13.8103 2.9010
red square false 48 77.5542 7.4670
purple triangle false 51 81.2290 8.5910
red square false 64 77.1991 9.5310
purple triangle false 65 80.1405 5.8240
yellow circle true 73 63.9785 4.2370
yellow circle true 87 63.5058 8.3350
purple square false 91 72.3735 8.2430
mlr head and mlr tail count records rather than lines. Whether you’re getting the first few records or the last few, the CSV header is included either way:
mlr --csv head -n 4 example.csv
color,shape,flag,index,quantity,rate
yellow,triangle,true,11,43.6498,9.8870
red,square,true,15,79.2778,0.0130
red,circle,true,16,13.8103,2.9010
red,square,false,48,77.5542,7.4670
mlr --csv tail -n 4 example.csv
color,shape,flag,index,quantity,rate
purple,triangle,false,65,80.1405,5.8240
yellow,circle,true,73,63.9785,4.2370
yellow,circle,true,87,63.5058,8.3350
purple,square,false,91,72.3735,8.2430
mlr --icsv --ojson tail -n 2 example.csv
{
"color": "yellow",
"shape": "circle",
"flag": true,
"index": 87,
"quantity": 63.5058,
"rate": 8.3350
}
{
"color": "purple",
"shape": "square",
"flag": false,
"index": 91,
"quantity": 72.3735,
"rate": 8.2430
}
You can sort on a single field:
mlr --icsv --opprint sort -f shape example.csv
color shape flag index quantity rate
red circle true 16 13.8103 2.9010
yellow circle true 73 63.9785 4.2370
yellow circle true 87 63.5058 8.3350
red square true 15 79.2778 0.0130
red square false 48 77.5542 7.4670
red square false 64 77.1991 9.5310
purple square false 91 72.3735 8.2430
yellow triangle true 11 43.6498 9.8870
purple triangle false 51 81.2290 8.5910
purple triangle false 65 80.1405 5.8240
Or, you can sort primarily alphabetically on one field, then secondarily numerically descending on another field, and so on:
mlr --icsv --opprint sort -f shape -nr index example.csv
color shape flag index quantity rate
yellow circle true 87 63.5058 8.3350
yellow circle true 73 63.9785 4.2370
red circle true 16 13.8103 2.9010
purple square false 91 72.3735 8.2430
red square false 64 77.1991 9.5310
red square false 48 77.5542 7.4670
red square true 15 79.2778 0.0130
purple triangle false 65 80.1405 5.8240
purple triangle false 51 81.2290 8.5910
yellow triangle true 11 43.6498 9.8870
If there are fields you don’t want to see in your data, you can use cut to keep only the ones you want, in the same order they appeared in the input data:
mlr --icsv --opprint cut -f flag,shape example.csv
shape flag
triangle true
square true
circle true
square false
triangle false
square false
triangle false
circle true
circle true
square false
You can also use cut -o to keep specified fields, but in your preferred order:
mlr --icsv --opprint cut -o -f flag,shape example.csv
flag shape
true triangle
true square
true circle
false square
false triangle
false square
false triangle
true circle
true circle
false square
You can use cut -x to omit fields you don’t care about:
mlr --icsv --opprint cut -x -f flag,shape example.csv
color index quantity rate
yellow 11 43.6498 9.8870
red 15 79.2778 0.0130
red 16 13.8103 2.9010
red 48 77.5542 7.4670
purple 51 81.2290 8.5910
red 64 77.1991 9.5310
purple 65 80.1405 5.8240
yellow 73 63.9785 4.2370
yellow 87 63.5058 8.3350
purple 91 72.3735 8.2430
You can use filter to keep only records you care about:
mlr --icsv --opprint filter '$color == "red"' example.csv
color shape flag index quantity rate
red square true 15 79.2778 0.0130
red circle true 16 13.8103 2.9010
red square false 48 77.5542 7.4670
red square false 64 77.1991 9.5310
mlr --icsv --opprint filter '$color == "red" && $flag == true' example.csv
color shape flag index quantity rate
red square true 15 79.2778 0.0130
red circle true 16 13.8103 2.9010
You can use put to create new fields which are computed from other fields:
mlr --icsv --opprint put '
$ratio = $quantity / $rate;
$color_shape = $color . "_" . $shape
' example.csv
color shape flag index quantity rate ratio color_shape
yellow triangle true 11 43.6498 9.8870 4.414868008496004 yellow_triangle
red square true 15 79.2778 0.0130 6098.292307692308 red_square
red circle true 16 13.8103 2.9010 4.760530851430541 red_circle
red square false 48 77.5542 7.4670 10.386259541984733 red_square
purple triangle false 51 81.2290 8.5910 9.455127458968688 purple_triangle
red square false 64 77.1991 9.5310 8.099790158430384 red_square
purple triangle false 65 80.1405 5.8240 13.760388049450551 purple_triangle
yellow circle true 73 63.9785 4.2370 15.09995279679018 yellow_circle
yellow circle true 87 63.5058 8.3350 7.619172165566886 yellow_circle
purple square false 91 72.3735 8.2430 8.779995147397793 purple_square
Even though Miller’s main selling point is name-indexing, sometimes you really want to refer to a field name by its positional index. Use $[[3]] to access the name of field 3 or $[[[3]]] to access the value of field 3:
mlr --icsv --opprint put '$[[3]] = "NEW"' example.csv
color shape NEW index quantity rate
yellow triangle true 11 43.6498 9.8870
red square true 15 79.2778 0.0130
red circle true 16 13.8103 2.9010
red square false 48 77.5542 7.4670
purple triangle false 51 81.2290 8.5910
red square false 64 77.1991 9.5310
purple triangle false 65 80.1405 5.8240
yellow circle true 73 63.9785 4.2370
yellow circle true 87 63.5058 8.3350
purple square false 91 72.3735 8.2430
mlr --icsv --opprint put '$[[[3]]] = "NEW"' example.csv
color shape flag index quantity rate
yellow triangle NEW 11 43.6498 9.8870
red square NEW 15 79.2778 0.0130
red circle NEW 16 13.8103 2.9010
red square NEW 48 77.5542 7.4670
purple triangle NEW 51 81.2290 8.5910
red square NEW 64 77.1991 9.5310
purple triangle NEW 65 80.1405 5.8240
yellow circle NEW 73 63.9785 4.2370
yellow circle NEW 87 63.5058 8.3350
purple square NEW 91 72.3735 8.2430
You can find the full list of verbs at the Reference: list of verbs page.
Multiple input files¶
Miller takes all the files from the command line as an input stream. But it’s format-aware, so it doesn’t repeat CSV header lines. For example, with input files (data/a.csv) and (data/b.csv), the system cat command will repeat header lines:
cat data/a.csv
a,b,c
1,2,3
4,5,6
cat data/b.csv
a,b,c
7,8,9
cat data/a.csv data/b.csv
a,b,c
1,2,3
4,5,6
a,b,c
7,8,9
However, mlr cat will not:
mlr --csv cat data/a.csv data/b.csv
a,b,c
1,2,3
4,5,6
7,8,9
Chaining verbs together¶
Often we want to chain queries together – for example, sorting by a field and taking the top few values. We can do this using pipes:
mlr --csv sort -nr index example.csv | mlr --icsv --opprint head -n 3
color shape flag index quantity rate
purple square false 91 72.3735 8.2430
yellow circle true 87 63.5058 8.3350
yellow circle true 73 63.9785 4.2370
This works fine – but Miller also lets you chain verbs together using the word then. Think of this as a Miller-internal pipe that lets you use fewer keystrokes:
mlr --icsv --opprint sort -nr index then head -n 3 example.csv
color shape flag index quantity rate
purple square false 91 72.3735 8.2430
yellow circle true 87 63.5058 8.3350
yellow circle true 73 63.9785 4.2370
As another convenience, you can put the filename first using --from. When you’re interacting with your data at the command line, this makes it easier to up-arrow and append to the previous command:
mlr --icsv --opprint --from example.csv sort -nr index then head -n 3
color shape flag index quantity rate
purple square false 91 72.3735 8.2430
yellow circle true 87 63.5058 8.3350
yellow circle true 73 63.9785 4.2370
mlr --icsv --opprint --from example.csv \
sort -nr index \
then head -n 3 \
then cut -f shape,quantity
shape quantity
square 72.3735
circle 63.5058
circle 63.9785
Sorts and stats¶
Now suppose you want to sort the data on a given column, and then take the top few in that ordering. You can use Miller’s then feature to pipe commands together.
Here are the records with the top three index values:
mlr --icsv --opprint sort -nr index then head -n 3 example.csv
color shape flag index quantity rate
purple square false 91 72.3735 8.2430
yellow circle true 87 63.5058 8.3350
yellow circle true 73 63.9785 4.2370
Lots of Miller commands take a -g option for group-by: here, head -n 1 -g shape outputs the first record for each distinct value of the shape field. This means we’re finding the record with highest index field for each distinct shape field:
mlr --icsv --opprint sort -f shape -nr index then head -n 1 -g shape example.csv
color shape flag index quantity rate
yellow circle true 87 63.5058 8.3350
purple square false 91 72.3735 8.2430
purple triangle false 65 80.1405 5.8240
Statistics can be computed with or without group-by field(s):
mlr --icsv --opprint --from example.csv \
stats1 -a count,min,mean,max -f quantity -g shape
shape quantity_count quantity_min quantity_mean quantity_max
triangle 3 43.6498 68.33976666666666 81.229
square 4 72.3735 76.60114999999999 79.2778
circle 3 13.8103 47.0982 63.9785
mlr --icsv --opprint --from example.csv \
stats1 -a count,min,mean,max -f quantity -g shape,color
shape color quantity_count quantity_min quantity_mean quantity_max
triangle yellow 1 43.6498 43.6498 43.6498
square red 3 77.1991 78.01036666666666 79.2778
circle red 1 13.8103 13.8103 13.8103
triangle purple 2 80.1405 80.68475000000001 81.229
circle yellow 2 63.5058 63.742149999999995 63.9785
square purple 1 72.3735 72.3735 72.3735
If your output has a lot of columns, you can use XTAB format to line things up vertically for you instead:
mlr --icsv --oxtab --from example.csv \
stats1 -a p0,p10,p25,p50,p75,p90,p99,p100 -f rate
rate_p0 0.0130
rate_p10 2.9010
rate_p25 4.2370
rate_p50 8.2430
rate_p75 8.5910
rate_p90 9.8870
rate_p99 9.8870
rate_p100 9.8870
File formats and format conversion¶
Miller supports the following formats:
CSV (comma-separared values)
TSV (tab-separated values)
JSON (JavaScript Object Notation)
PPRINT (pretty-printed tabular)
XTAB (vertical-tabular or sideways-tabular)
NIDX (numerically indexed, label-free, with implicit labels
"1","2", etc.)DKVP (delimited key-value pairs).
What’s a CSV file, really? It’s an array of rows, or records, each being a list of key-value pairs, or fields: for CSV it so happens that all the keys are shared in the header line and the values vary from one data line to another.
For example, if you have:
shape,flag,index
circle,1,24
square,0,36
then that’s a way of saying:
shape=circle,flag=1,index=24
shape=square,flag=0,index=36
Other ways to write the same data:
CSV PPRINT
shape,flag,index shape flag index
circle,1,24 circle 1 24
square,0,36 square 0 36
JSON XTAB
{ shape circle
"shape": "circle", flag 1
"flag": 1, index 24
"index": 24 .
} shape square
{ flag 0
"shape": "square", index 36
"flag": 0,
"index": 36
}
DKVP
shape=circle,flag=1,index=24
shape=square,flag=0,index=36
Anything we can do with CSV input data, we can do with any other format input data. And you can read from one format, do any record-processing, and output to the same format as the input, or to a different output format.
How to specify these to Miller:
If you use
--csvor--jsonor--pprint, etc., then Miller will use that format for input and output.If you use
--icsvand--ojson(note the extraiando) then Miller will use CSV for input and JSON for output, etc. See also Keystroke-savers for even shorter options like--c2j.
You can read more about this at the File formats page.
Choices for printing to files¶
Often we want to print output to the screen. Miller does this by default, as we’ve seen in the previous examples.
Sometimes, though, we want to print output to another file. Just use > outputfilenamegoeshere at the end of your command:
mlr --icsv --opprint cat example.csv > newfile.csv
# Output goes to the new file;
# nothing is printed to the screen.
cat newfile.csv
color shape flag index quantity rate
yellow triangle true 11 43.6498 9.8870
red square true 15 79.2778 0.0130
red circle true 16 13.8103 2.9010
red square false 48 77.5542 7.4670
purple triangle false 51 81.2290 8.5910
red square false 64 77.1991 9.5310
purple triangle false 65 80.1405 5.8240
yellow circle true 73 63.9785 4.2370
yellow circle true 87 63.5058 8.3350
purple square false 91 72.3735 8.2430
Other times we just want our files to be changed in-place: just use mlr -I:
cp example.csv newfile.txt
cat newfile.txt
color,shape,flag,index,quantity,rate
yellow,triangle,true,11,43.6498,9.8870
red,square,true,15,79.2778,0.0130
red,circle,true,16,13.8103,2.9010
red,square,false,48,77.5542,7.4670
purple,triangle,false,51,81.2290,8.5910
red,square,false,64,77.1991,9.5310
purple,triangle,false,65,80.1405,5.8240
yellow,circle,true,73,63.9785,4.2370
yellow,circle,true,87,63.5058,8.3350
purple,square,false,91,72.3735,8.2430
mlr -I --csv sort -f shape newfile.txt
cat newfile.txt
color,shape,flag,index,quantity,rate
red,circle,true,16,13.8103,2.9010
yellow,circle,true,73,63.9785,4.2370
yellow,circle,true,87,63.5058,8.3350
red,square,true,15,79.2778,0.0130
red,square,false,48,77.5542,7.4670
red,square,false,64,77.1991,9.5310
purple,square,false,91,72.3735,8.2430
yellow,triangle,true,11,43.6498,9.8870
purple,triangle,false,51,81.2290,8.5910
purple,triangle,false,65,80.1405,5.8240
Also using mlr -I you can bulk-operate on lots of files: e.g.:
mlr -I --csv cut -x -f unwanted_column_name *.csv
If you like, you can first copy off your original data somewhere else, before doing in-place operations.
Lastly, using tee within put, you can split your input data into separate files per one or more field names:
mlr --csv --from example.csv put -q 'tee > $shape.".csv", $*'
cat circle.csv
color,shape,flag,index,quantity,rate
red,circle,true,16,13.8103,2.9010
yellow,circle,true,73,63.9785,4.2370
yellow,circle,true,87,63.5058,8.3350
cat square.csv
color,shape,flag,index,quantity,rate
red,square,true,15,79.2778,0.0130
red,square,false,48,77.5542,7.4670
red,square,false,64,77.1991,9.5310
purple,square,false,91,72.3735,8.2430
cat triangle.csv
color,shape,flag,index,quantity,rate
yellow,triangle,true,11,43.6498,9.8870
purple,triangle,false,51,81.2290,8.5910
purple,triangle,false,65,80.1405,5.8240