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

"Invalid .internal.selfref detected and fixed by taking a copy..."

No need to make a copy when assigning id2 within f2() you can add a column directly by altering:

# From:

      x <- x[, id2 := which(vapply(groups, function(x,y) any(x==y), .BY[[1]], FUN.VALUE=T)), by=id]

# To something along the lines of:
      x$id2 <- findInterval( match( x$id, unlist(groups)), cumsum(c(0,sapply(groups, length)))+1)

Then you can continue use your 'x' data.table like normal without incurring a warning.

Also, to simply suppress the warning you can use suppressWarnings() around the f2(x[["res"]]) call.

Even on small tables there can be substantial performance difference:

Performance Comparison:
Unit: milliseconds
                       expr      min       lq   median       uq      max neval
                   f.main() 2.896716 2.982045 3.034334 3.137628 7.542367   100
 suppressWarnings(f.main()) 3.005142 3.081811 3.133137 3.210126 5.363575   100
            f.main.direct() 1.279303 1.384521 1.413713 1.486853 5.684363   100