CJ can handle list() input if sorted=FALSE but fails confusingly

[MichaelChirico]

CJ(1:2, list(1:3, 1))

Error in forderv(y, retGrp = TRUE) :
Column 2 is length 1 which differs from length of column 1 (3)

CJ_old(1:2, list(1:3, 1), sorted = FALSE)
   V1    V2
1:  1 1,2,3
2:  1     1
3:  2 1,2,3
4:  2     1

The logic for building the CJ output from list input is the same, but sorted has to be FALSE because there's no ordering of lists.

We can either stop here or force sorted = FALSE... either way the current behavior is confusing.

[jangorecki]

I don't think we need to support list. There was idea to make it generic so there can be data.table method... #1717 (comment)

[MichaelChirico]

we don't need to support it, but it's also extremely easy to build in the current logic as well as that in #3596.