get breaks .SDcols
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Assessment
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Newbie friendliness
- 35/100
Research direction
Start by running the issue's reproducible data.table example and inspect the evaluation of .SDcols = xnm inside the nested expression using get(active). Confirm that .SD includes r despite the selected columns; done means the example no longer reports four rows, while the explicitly selected x1:x3 behavior remains correct.
Written by the indexing model from the issue text.
Description
This may be related to #2036 and/or #1548. Sorry for the over-long example, the last command is the one that matters:
library(data.table)
iris = data.table(iris)
iris = iris[ , !'Species']
iris[ , (names(iris)) := lapply(.SD, function(x) {
(x - mean(x))/sd(x)
})]
xnm = c('x1', 'x2', 'x3')
setnames(iris, c('y', xnm))
y = iris$y
iris[ , c('r', 'y') := .(y, NULL)]
all_cor = iris[ , sapply(.SD, cor, r), .SDcols = xnm]
active = names(which.max(abs(all_cor)))
path = seq(0, all_cor[active], length.out = 100L)
cor_path = sapply(path, function(beta) {
iris[ , { print(length(.SD))
sapply(.SD, cor, r - beta*get(active))
}, .SDcols = xnm]
})
Despite explicitly setting .SDcols = xnm (i.e., x1:x3), .SD has picked up r again (as seen from nrow(cor_path) == 4L.
If we replace get(active) with its current value (x2), the code works as expected. The fix of #1548 (to set envir = as.environment(.SD)) doesn't work here.
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