built-in ifelse [R for BE/BA]

posted by mittyri – Russia, 2019-04-30 11:05  – Posting: # 20263
Views: 2,675

(edited by mittyri on 2019-04-30 11:17)

Hi ElMaestro,

please see ifelse internals:
function (test, yes, no)
{
  if (is.atomic(test)) {
    if (typeof(test) != "logical")
      storage.mode(test) <- "logical"
    if (length(test) == 1 && is.null(attributes(test))) {
      if (is.na(test))
        return(NA)
      else if (test) {
        if (length(yes) == 1) {
          yat <- attributes(yes)
          if (is.null(yat) || (is.function(yes) && identical(names(yat),
            "srcref")))
            return(yes)
        }
      }
      else if (length(no) == 1) {
        nat <- attributes(no)
        if (is.null(nat) || (is.function(no) && identical(names(nat),
          "srcref")))
          return(no)
      }
    }
  }
  else test <- if (isS4(test))
    methods::as(test, "logical")
  else as.logical(test)
  ans <- test
  ok <- !is.na(test)
  if (any(test[ok]))
    ans[test & ok] <- rep(yes, length.out = length(ans))[test & ok]
  if (any(!test[ok]))
    ans[!test & ok] <- rep(no, length.out = length(ans))[!test & ok]
  ans
}


That's why Hadley implemented his own if_else function. Your one if in f2 is substituted to many of in f1. And the last part is two separated actions for 'No' and 'Yes'.
So you can write your own ifelse function (for your own purposes) which will be much faster than the built-in

And the winner is
f3 = function(x, Len)
{
  rslt=rep("foo", Len)
  rslt[which(x==1, arr.ind = T)]="bar"
  return(rslt)
}

Kind regards,
Mittyri

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