Elegantly assigning multiple columns in data.table with lapply()

Question

I am trying to figure out an elegant way to use := assignment to replace many columns at once in a data.table by applying a shared function. A typi

Answer 1

Is this what you are looking for?

dt[ , names(dt)[20:100] :=lapply(.SD, function(x) sqrt(x) ) , .SDcols=20:100]

I have heard tell that using .SD is not so efficient because it makes a copy of the table beforehand, but if your table isn't huge (obviously that's relative depending on your system specs) I doubt it will make much of a difference.