Invalid .internal.selfref in data.table

Question

I needed to assign a \"second\" id to group some values inside my original id. this is my sample data:

dt<-structure(list(id = c(\"aaaa\", \"         


        

Answer 1

Yes, the problem is the list. Here is a simple example:

DT <- data.table(1:5)
mylist1 <- list(DT,"a")
mylist1[[1]][,id:=.I]
#warning

mylist2 <- list(data.table(1:5),"a")
mylist2[[1]][,id:=.I]
#no warning

You should avoid copying a data.table into a list (and to be on the safe side I would avoid having a DT in a list at all). Try this:

f1 <- function(){
  mylist <- list(res=data.table(id = c("aaaa", "aaaa", "aaas", "aaas", "bbbb", "bbbb"),
                 period = c("start", "end", "start", "end", "start", "end"),
                 date = structure(c(15401L, 15401L, 15581L, 15762L, 15430L, 15747L), class = c("IDate", "Date"))))
  other_results <- ""
  mylist$other_results <- other_results
  mylist
}