Reference `data.table` column by name

Question

Suppose there is:

DT = data.table(a=1, b=2, "a+b"=8)

and there is variable col="a+b" referencing the third column of DT

How to perform an operation on that column by reference? Let's say I want multiply col by 2, so in the above example the result should be 8*2=16, not (1+2)*2=6

For example, this obviously doesn't work:

DT[, c:=as.name(col)*2]

Answer 1

It sounds like you're looking for get:

DT = data.table(a=1, b=2, "a+b"=8)
col = "a+b"
DT[, get(col) * 2]
# [1] 16
DT[, c := get(col) * 2]
DT
#    a b a+b  c
# 1: 1 2   8 16