Row-wise sort then concatenate across specific columns of data frame

Question

(Related question that does not include sorting. It\'s easy to just use paste when you don\'t need to sort.)

I have a less-than-ideally-structured tabl

Answer 1

My first thought would've been to do this:

dt[, new_var := paste(sort(.SD), collapse = ", "), by = 1:nrow(dt)]

But you could make your function work with a couple of simple modifications:

f = function(...) paste(c(...)[order(c(...))],collapse=", ")

dt[, new_var := do.call(function(...) mapply(f, ...), .SD)]