[R] inefficient ifelse() ?

From: ivo welch <ivowel_at_gmail.com>
Date: Tue, 01 Mar 2011 14:19:26 -0500

dear R experts---

  t <- 1:30
  f <- function(t) { cat("f for", t, "\n"); return(2*t) }
  g <- function(t) { cat("g for", t, "\n"); return(3*t) }
  s <- ifelse( t%%2==0, g(t), f(t))

shows that the ifelse function actually evaluates both f() and g() for all values first, and presumably then just picks left or right results based on t%%2. uggh... wouldn't it make more sense to evaluate only the relevant parts of each vector and then reassemble them?


Ivo Welch

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