dot alias not understood as expected in by/keyby
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Assessment
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Newbie friendliness
- 35/100
Research direction
Start with the reproducible DT[...] examples and inspect the [.data.table evaluation paths for by/keyby and j. Compare how . is handled in each context, then add regression coverage showing that the by expression evaluates consistently with the working j example.
Written by the indexing model from the issue text.
Description
I think there are a couple of issues on similar fronts addressing that we should be more consistent about how/when . is understood in data.table and more specifically within [.data.table calls. Here's a new one I came across today:
DT = data.table(a = 1:10, b = 10:1)
DT[ , mean(b), by = {
a2 = a^2
.(a2mod5 = a2 %% 5)
}]
This returns an error since evaluation looks for the . function (i.e., the call has not replaced . with list) (replacing . with list, this evaluates as expected):
Error in .(b2mod5 = b2%%5) : could not find function "."
Contrast this to something similar in j:
DT = data.table(a = 1:10, b = 10:1)
DT[ , {
b2 = b^2
.(b2mod5 = sum(b2 %% 5))
}, by = a %% 3]
# a b2mod5
# 1: 1 6
# 2: 2 6
# 3: 0 8
Some related issues: #2391, #1912, #852, a few others I can't find just now
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