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

Just apply down rows:

apply(df,1,function(x){
  paste(sort(x),collapse = ",")
})

Wrap it in a function if you want. You'll either have to define which columns to send or assume all. i.e. apply(df[ ,2:3],1,f()...

sort(x) is the same as x[order(x)]

Answer 2

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)]