How to delete a row by reference in data.table?

Question

My question is related to assignment by reference versus copying in data.table. I want to know if one can delete rows by reference, similar to

Answer 1

Here is a working function based on @vc273's answer and @Frank's feedback.

delete <- function(DT, del.idxs) {           # pls note 'del.idxs' vs. 'keep.idxs'
  keep.idxs <- setdiff(DT[, .I], del.idxs);  # select row indexes to keep
  cols = names(DT);
  DT.subset <- data.table(DT[[1]][keep.idxs]); # this is the subsetted table
  setnames(DT.subset, cols[1]);
  for (col in cols[2:length(cols)]) {
    DT.subset[, (col) := DT[[col]][keep.idxs]];
    DT[, (col) := NULL];  # delete
  }
   return(DT.subset);
}

And example of its usage:

dat <- delete(dat,del.idxs)   ## Pls note 'del.idxs' instead of 'keep.idxs'

Where "dat" is a data.table. Removing 14k rows from 1.4M rows takes 0.25 sec on my laptop.

> dim(dat)
[1] 1419393      25
> system.time(dat <- delete(dat,del.idxs))
   user  system elapsed 
   0.23    0.02    0.25 
> dim(dat)
[1] 1404715      25
> 

PS. Since I am new to SO, I could not add comment to @vc273's thread :-(