Do you reassign == and != to isTRUE( all.equal() )?

Question

A previous post prompted me to post this question. It would seem like a best-practice to reassign == to isTRUE(all.equal()) ( and !=

Answer 1

As @joran alluded to, you'll run into floating point issues with == and != in pretty much any other language too. One important aspect of them in R is the vectorization part.

It would be much better to define a new function almostEqual, fuzzyEqual or similar. It is unfortunate that there is no such base function. all.equal isn't very efficient since it handles all kinds of objects and returns a string describing the difference when mostly you just want TRUE or FALSE.

Here's an example of such a function. It's vectorized like ==.

almostEqual <- function(x, y, tolerance=1e-8) {
  diff <- abs(x - y)
  mag <- pmax( abs(x), abs(y) )
  ifelse( mag > tolerance, diff/mag <= tolerance, diff <= tolerance)
}

almostEqual(1, c(1+1e-8, 1+2e-8)) # [1]  TRUE FALSE

...it is around 2x faster than all.equal for scalar values, and much faster with vectors.

x <- 1
y <- 1+1e-8
system.time(for(i in 1:1e4) almostEqual(x, y)) # 0.44 seconds
system.time(for(i in 1:1e4) all.equal(x, y))   # 0.93 seconds