Keyed lookup on data.table without 'with'

Question

I have a data.table structure like so (except mine is really huge):

dt <- data.table(x=1:5, y=3:7, key=\'x\')

I want to loo

Answer 1

New answer, now that I think I understand what was requested:

> X <- data.table(x=x)
> merge(dt, X)
   x y
1: 3 6
2: 4 7