[R-Forge #5585] DT[, list(list(.)), by=.] returns wrong results in R-3.1.0.

[arunsrinivasan]

Submitted by: Arun ; Assigned to: Nobody; R-Forge link

require(data.table)
DT <- data.table(x=c(1,2,2,3,3,3), y=10:15)
DT[, print(list(list(.I))), by=x] ## prints fine.
# [[1]]
# [[1]][[1]]
# [1] 1
# 
# [[1]]
# [[1]][[1]]
# [1] 2 3
# 
# [[1]]
# [[1]][[1]]
# [1] 4 5 6
# 
# Empty data.table (0 rows) of 1 col: x

DT[, list(list(.I)), by=x] ## all points to last grouping variable
#    x    V1
#1: 1 4,5,6
#2: 2 4,5,6
#3: 3 4,5,6

The issue goes away if . is wrapped with I(.) or any other function for that matter.

## works fine.
DT[, list(list(I(.I))), by=x]
DT[, list(list(sum(y))), by=x]

[arunsrinivasan]

update: fixed in commit 1311, 5e2ced0. All good!

Just realised that this only fixes this case, but not DT[, z := list(list(y)), by=x]. Will reopen and fix soon.