How to apply same function to every specified column in a data.table

Question

I have a data.table with which I\'d like to perform the same operation on certain columns. The names of these columns are given in a character vector. In this particular ex

Answer 1

library(data.table)
(dt <- data.table(a = 1:3, b = 1:3, d = 1:3))

Hence:

   a b d
1: 1 1 1
2: 2 2 2
3: 3 3 3

Whereas (dt*(-1)) yields:

    a  b  d
1: -1 -1 -1
2: -2 -2 -2
3: -3 -3 -3