[R-Forge #2588] New warning needed when items on RHS of := are silently ignored

[arunsrinivasan]

Submitted by: Matt Dowle; Assigned to: Nobody; R-Forge link

As raised here on SO.

[MichaelChirico]

The "unexpected" version in the So link now returns the "expected" results:

dt <- data.table(x=c(1:10))
setkey(dt, x)

k <- data.table(x=c(1:5,10), b=c(letters[1:5], "d"))
setkey(k, x)

dt[,b:=k[.BY, list(b)],by=x][]
        x      b
 1:     1      a
 2:     2      b
 3:     3      c
 4:     4      d
 5:     5      e
 6:     6   <NA>
 7:     7   <NA>
 8:     8   <NA>
 9:     9   <NA>
10:    10      d

[MichaelChirico]

I think current logic assumes you were trying to build list columns if you pass an over-sized list in RHS:

DT = data.table(a = 1:3)
DT[ , c := .(2, 3)]

Error in [.data.table(DT, , :=(c, .(2, 3))) :
Supplied 2 items to be assigned to 3 items of column 'c'. If you wish to 'recycle' the RHS please use rep() to make this intent clear to readers of your code.

DT[ , c('b', 'c') := .(rep(0, 3), rep(1, 3), rep(2, 3))]

Error in [.data.table(DT, , :=(c("b", "c"), .(rep(0, 3), rep(1, 3), :
Supplied 2 columns to be assigned 3 items. Please see NEWS for v1.12.2. Try adding/removing a list() or .() wrapper around the RHS.

So I guess this is covered by more recent updates.