Dynamically add column names to data.table when aggregating

Question

I know we can dynamically add column names when creating columns by reference (using :=), as described e.g. here: Dynamic column names in data.table.

Ho

Answer 1

As mentioned in the comments by lukeA, setNames can be used:

m <- c("blah", "foo")
test_dtb[ , setNames(list(mean(b), median(b)), m), by = id] 

Answer 2

Just make sure data.table knows "m" is not a variable name.

Parentheses or "c" will do.

test_dtb[, (m)  := mean(b),by = id]
test_dtb[, c(m) := mean(b),by = id]