* Allow step -a shift_lag/shift_lead/delta/ratio to specify records back/forward (#1002)
Extends the slwin_m_n naming convention to more steppers: shift_lag_12
refers 12 records back, shift_lead_4 refers 4 records forward, and
likewise delta_N, ratio_N, and shift_N. The unsuffixed forms keep their
existing 1-record-back/forward behavior and output field names.
Backward-looking steppers cache copies of previous values in a
fixed-size ring buffer (tValueRing) in their own state, following the
existing pattern of not reading from the window keeper's already-emitted
records, to avoid races with downstream transformers. shift_lead_N uses
the existing forward-window machinery shared with slwin.
Also adds nil guards to all steppers' process functions for the case
where the record at the window center lacks the stepped field, which
previously panicked (pre-existing on main, e.g.
"mlr step -a delta,shift_lead -f x" or "-a slwin_1_1" over
heterogeneous data), and which the new parameterized combinations make
easier to reach.
Includes unit tests, regression cases 0024-0027, and regenerated help
text / docs / man page.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
* Clarify step -a help text: both plain and _{n} stepper forms are valid (#1002)
Per review on #2190: descriptions like "E.g. delta_7 for 7 records
back" read as if the suffixed form were the only syntax. Reword the
shift, shift_lag, shift_lead, delta, and ratio descriptions to state
both forms explicitly -- e.g. "Use delta or equivalently delta_1 for
the previous record, or delta_{n} for n records back" -- using the {n}
placeholder style, and update the matching usage paragraph and
reference-verbs prose. Regenerate help-derived docs, man page, and
cli-help regression expectation.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
* Give a specific error for invalid stepper count suffixes (#1002)
Per review on #2190: "mlr step -a delta_0" (or delta_-1, delta_x, etc.)
previously reported the generic 'stepper "delta_0" not found'. Now,
when the name prefixes a known count-suffix stepper (shift, shift_lag,
shift_lead, delta, ratio) but the suffix is not a positive integer, the
error is:
mlr step: stepper "delta_0": count must be a positive integer
Truly unknown stepper names keep the existing "not found" message.
Adds should-fail regression cases for delta_0 and delta_-1, and unit
tests for the detection helper.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
---------
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
Logic for transforming input records into output records as requested by the user (sort, filter, etc.).:
The IRecordTransformer abstract record-transformer interface datatype, as well as the ChainTransformer Go-channel chaining mechanism for piping one transformer into the next.
The transformer lookup table, used for Miller command-line parsing, verb construction, and online help.
All the concrete record-transformers such as cat, tac, sort, put, and so on.
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