What is the best practice to delete columns programmatically in data.table?
The following works:
DT[, c("a", "b") := NULL]
But when trying to do this using a variable that stores column names
cols.to.del <- c("a", "b")
DT[, cols.to.del := NULL]
it fails badly as cols.to.del is not evaluated in the correct environment.
We can wrap it inside the brackets, and then assign (:=) to 'NULL' (preferred way)
DT[, (cols.to.del) := NULL]
Or another option (in case we don't want to wrap it with brackets) would be to loop over the 'cols.to.del' in a for loop and assign to NULL
for(j in seq_along(cols.to.del)){
DT[, cols.to.del[j] := NULL]
}
Or for subsetting the columns, we can use setdiff along with with=FALSE.
DT[, setdiff(names(DT), cols.to.del), with=FALSE]
DT; rather the output of that command is a new data.table which you must assign (by copying) to DT, which is likely inefficient.