i doing this:   myfun <- function(inputvar_vec){ # inputvar_vec input vector # # result = output vector return(result) }  dt[, result := lapply(.sd, myfun), = byvar, .sdcols = inputvar]   i getting following warning:   warning message: `in `[.data.table`(df1, , `:=`(prop, lapply(.sd, propeventinlastk)),  : invalid .internal.selfref detected , fixed taking copy of whole table,      := can add new column reference. @ earlier point,  data.table has been copied r (or been created manually using structure()  or similar). (and more stuff) .... `   my guess because stacking result  vectors (after operation), copy being made?   can suggest method remove warning? have done using apply functions , thought should extendable here too.   my other question is: can pass chunk of rows data frame (subsetted using statement), , call function myfun operate on that?   adding example requested   # generate data n = 10000 default=na value = 1 df = data.table(id = sample(1:5000, n, replace=true),     ...
 
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