data.table making a copy of table in R -

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),                 trial = sample(c(0,1,2), n, replace=true),                 ts = sample(1:200, n, replace=true))  #set keys setkeyv(df, c("id", "ts"))  df[["trial"]] = as.numeric(df[["trial"]]==value)  testfun <- function(x){   l=length(x)   x = x[l:1]   x = fts(data=x)   y = rep(default, l)   if(l>=k){     y1 = as.numeric(moving.sum(x,k))     y = c(y1, rep(default,l-length(y1)))   }    return(y[l:1]/k) }  df[, prop:= lapply(.sd, testfun), = id, .sdcols = "trial"] 

still getting same warning message:

warning message: in `[.data.table`(df, , `:=`(prop, lapply(.sd, testfun)), = id,  :   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). avoid key<-, names<- , attr<- in r (and oddly) may copy whole data.table. use set* syntax instead avoid copying: setkey(), setnames() , setattr(). also, list(dt1,dt2) copy entire dt1 , dt2 (r's list() copies named objects), use reflist() instead if needed (to implemented). if message doesn't help, please report datatable-help root cause can fixed. 

the issue arises in

df[["trial"]] = as.numeric(df[["trial"]]==value) 

which not data.table approach

a data.table approach use :=

 df[, trial := as.numeric(trial == value)] 

should avoid issue.

understanding why copies made (and internal self references may voided) see understanding when data.table reference (vs copy of) data.table

it important realize there no [[<- method data.tables , [[<-.data.frame called, copy entire object , not of careful things data.table method (such [<-.data.table) (returning valid data.table.