How do you remove columns from a data.frame?

I use data.table's := operator to delete columns instantly regardless of the size of the table.

DT[, coltodelete := NULL]

or

DT[, c("col1","col20") := NULL]

or

DT[, (125:135) := NULL]

or

DT[, (variableHoldingNamesOrNumbers) := NULL]

Any solution using <- or subset will copy the whole table. data.table's := operator merely modifies the internal vector of pointers to the columns, in place. That operation is therefore (almost) instant.

To delete single columns, I'll just use dat$x <- NULL.

To delete multiple columns, but less than about 3-4, I'll use dat$x <- dat$y <- dat$z <- NULL.

For more than that, I'll use subset, with negative names (!):

subset(mtcars, , -c(mpg, cyl, disp, hp))