Select / assign to data.table when variable names are stored in a character vector

Question

How do you refer to variables in a data.table if the variable names are stored in a character vector? For instance, this works for a data.frame:

Answer 1

Retrieve multiple columns from data.table via variable or function:

library(data.table)

x <- data.table(this=1:2,that=1:2,whatever=1:2)

# === explicit call
x[, .(that, whatever)]
x[, c('that', 'whatever')]

# === indirect via  variable
# ... direct assignment
mycols <- c('that','whatever')
# ... same as result of a function call
mycols <- grep('a', colnames(x), value=TRUE)

x[, ..mycols]
x[, .SD, .SDcols=mycols]

# === direct 1-liner usage
x[, .SD, .SDcols=c('that','whatever')]
x[, .SD, .SDcols=grep('a', colnames(x), value=TRUE)]

which all yield

   that whatever
1:    1        1
2:    2        2

I find the .SDcols way the most elegant.