sampled.js

function sampled(arr, size) {
  var sampled = [], i, n, idx, l = arr.length;
  if (arr.length <= size){
    return arr
  } else {
    for (i = 0; i < size; i++) {
      n = (i / size) * l;
      // faster Math.ceil (because I'm doing this with large arrays inside raf)
      idx = (n << 0);
      idx = (idx == n)? idx: idx + 1;
      sampled[i] = arr[idx];
    }
    return sampled;
  }
}

var letters = 'a b c d e f g h i j k l m n o p'.split(' ');

sampled(letters, 5); // a e h k n
sampled(letters, 10); // a c e f h i k m n p

// TODO I would like this to expand out to fill all the available space - but that's a nice to have
sampled(letters, 100); // a b c d e f g h i j k l m n o p