with = FALSE silently ignores by

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
45/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
r
Domain
data

Research direction

Start by reproducing the issue's data.table examples with with = FALSE and by = id, then compare the result with the .SD example. Decide whether the intended fix is to honor by or warn that it is ignored, and update the relevant behavior and documentation accordingly. Add a regression check showing the chosen behavior.

Written by the indexing model from the issue text.

Description

bug

Using with = FALSE with a by argument will result in the by argument being silently ignored:

library(data.table)
dt = data.table(id = rep(3:2, 2L), y = 1:4)
dt[, 1:2, by = id, with = FALSE]
#>       id     y
#>    <int> <int>
#> 1:     3     1
#> 2:     2     2
#> 3:     3     3
#> 4:     2     4
dt[, .SD, by = id]
#>       id     y
#>    <int> <int>
#> 1:     3     1
#> 2:     3     3
#> 3:     2     2
#> 4:     2     4

Expected behavior would either be:

  1. A warning that by= is ignored and update with documentation; or
  2. The by argument is used.

I lean towards option 2 but I feel like this is an infrequent use case and that option 1 is easier to implement. I could do a PR if there's a preferred route.

Dominant language
R
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Merged PRs (30d)
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