:= together with by=.EACHI doesn't add new column if no rows match

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Assessment

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

Research direction

Start by running the reproducible R example against data.table, focusing on the := assignment with a join and by=.EACHI when no rows match. Done means the assignment adds the new column, consistent with the preceding examples, and a regression test covers this no-match case.

Written by the indexing model from the issue text.

Description

bug joins 
require(data.table) # Mar 20 2018 devel
dt <- data.table(x=1:5); dt
#    x
# 1: 1
# 2: 2
# 3: 3
# 4: 4
# 5: 5
dt[x %in% 6:7, y := 2L]; dt # works as expected when no rows match in `i`
#    x  y
# 1: 1 NA
# 2: 2 NA
# 3: 3 NA
# 4: 4 NA
# 5: 5 NA
dt[.(x=6:7), on="x", z := 2L]; dt # same here.. works as expected
#    x  y  z
# 1: 1 NA NA
# 2: 2 NA NA
# 3: 3 NA NA
# 4: 4 NA NA
# 5: 5 NA NA

# BUG
dt[.(x=6:7), on="x", by=.EACHI, w := 2L]; dt # doesn't add 'w' col
#    x  y  z
# 1: 1 NA NA
# 2: 2 NA NA
# 3: 3 NA NA
# 4: 4 NA NA
# 5: 5 NA NA
Dominant language
R
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