[R-Forge #5571] complicated by expression can hide column if .SD is present

[arunsrinivasan]

Submitted by: Eduard Antonyan; Assigned to: Nobody; R-Forge link

A bunch of specific things have to happen for this bug - when the by expression includes a column, that column disappears in the j-expression if .SD is also used in the j-expression:

require(data.table)
dt = data.table(a = 1, b = 1)
dt[, data.table(a, .SD), by = cumsum(a)]
# Error in data.table(a, .SD) : object 'a' not found

Expressions that work:

dt[, data.table(a, .SD), by = a]
dt[, data.table(b, .SD), by = cumsum(a)]
dt[, data.table(a, b), by = cumsum(a)]

[MichaelChirico]

Should be a lot easier to handle now that we've got .SDall, right?