[R-Forge #5659] key is not retained after join on factor columns

[arunsrinivasan]

Submitted by: Gerhard Nachtmann; Assigned to: Nobody; R-Forge link

Description here.

[arunsrinivasan]

It's not just on factor columns. It's basically due to recent changes in 1.9.3 in this part of [.data.table:

if (haskey(x)) {
    keylen = which.first(!key(x) %chin% ansvars)-1L
    if (is.na(keylen)) keylen = length(key(x))
    if (keylen > length(rightcols) && !.Call(CisOrderedSubset, irows, nrow(x))) keylen = length(rightcols)
    if (keylen && ((is.data.table(i) && haskey(i)) || is.logical(i) || .Call(CisOrderedSubset, irows, nrow(x))))
        setattr(ans,"sorted",head(key(x),keylen))
}

Here CisOrderedSubset doesn't provide required result when there's NA (IIRC from debugging it sometime back).

And IIUC, this is how it was before.

[nachti]

Thanks for the migration from R-Forge!