Question

In reading R for programmers I saw this function

oddcount <- function(x) {
  k <- 0
  for (n in x) {
    if (n %% 2 == 1) k <- k+1
  }
  return(k)
}

I would prefer to write it in a simpler style (i.e in lisp)

(defn odd-count [xs]
  (count (filter odd? xs)))

I see the function length is equivalent to count and I can write odd? so are there built-in map/filter/remove type functions?

Answer 1

A more R way to doing this would be to avoid the for loop, and use vectorization:

oddcount <- function(x) {
  sum(x %% 2)
}

The comparison between x and 2 outputs a vector as x itself is a vector. Sum than calculates the sum of the vector, where TRUE equals 1 and FALSE equals zero. In this way the function calculates the number of odd numbers in the vector.

This already leads to more simple syntax, although for non-vectorization-oriented people the for loop tends to be easier to read. I greatly prefer the vectorized syntax as it is much shorter. I would prefer to use a more descriptive name for x though, e.g. number_vector.