In below example, I need to assign a list to a data.table's variable code, so that value list(11,22) is assigned to dt$code. How do I do that?
dt <- data.table(1:3)
dt$code <- list()
dt[V1==2, code:=list(11,22)] # does not work
dt[V1==2, code:=.(list(11,22))] # does not work
My question is simpler and shorter than in the earlier post. Thanks for the answer:
dt[V1==2, code:=list(list((list(11,22)))] # works !
dt[V1==2, code:=list(list(list(11,22)))] # works !
This can also be written as
dt[V1==2, code:=.(.(.(11,22)))]
which is actually synonymous to
dt[V1==2, code:=.(.(c(11,22)))]
Note however that in this case, it is a vector, rather than list, that is assigned to variable code for V1==2.
Note also that it is not possible (as of yet) to do either of these:
dt[all(code==c(11,22))]
dt[, ifelse(all(code==c(11,22)), T, F)]
which negates quite abit the value of using vectors as variable types for data.table.
PS. Added - as per Matt's comment below
The new development release of data.table will make this question obsolete. Starting from 1.12.3 release, it will be possible to write either way including dt[V1==2, code:=list(11,22)].
dt[code==list(list(list(11,22)))] ? (this would really boost the use of lists within data.table)> DT[2, B:=letters[9:13]] # was error, now works > DT[2, B:=.(letters[9:13])] # was error, now works > DT[2, B:=.(list(letters[9:13]))] # .(list()) was needed, still works. Would it however be possible to do this: DT[B==letters[9:13]] ?DT[B==letters[9:13]] is technically possible as a vector scan but are you really sure that a multi-column key (or index) is not more appropriate; e.g. setkey(DT, id1, id2, id3, id4, id5); DT[as.list(letters[9:13)]] ?
dt[V1 == 2, code := list(list(list(11, 12)))]. possible duplicate of stackoverflow.com/questions/22531477/…