deprecate multiple columns to be defined as scalar character

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#4,357 15 comments 5 reactions 0 assignees View on GitHub

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
35/100
Issue type
Refactor
Clarity
Mostly clear
Activity status
Stale
Tech stack
r
Domain
data

Research direction

Start by tracing the key and setkey arguments in data.table, then inspect by and keyby in [.data.table. Identify related scalar character paths beyond the two examples, review existing coverage for these arguments, and define completion as consistently requiring c("A", "B") for multiple columns.

Written by the indexing model from the issue text.

Description

breaking-change consistency

For now I identified two cases, there are probably some more:

  • key argument in data.table should not accept key="A,B", which implies that setkey should not accept it as well
  • by argument in [.data.table should not accept by="A,B" (so keyby)

In both cases c("A","B") should be used instead.
I understand that it has been added as a nice feature that makes life (very little bit) simpler, but it breaks consistency, introduces new challenges (#4292), and it is also confusing to users (like does the column has a comma in its name?).
WDUT @mattdowle

Dominant language
R
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