sampled.js

function sampled(arr, size){
    if(arr.length <= size){
        return arr
    } else {
        var sampled = [];
        for(var i = 0; i < size; i++){
            var idx = Math.ceil((i / size) * arr.length);
            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
sampled(letters, 100); // a b c d e f g h i j k l m n o p