Counting the occurrences / frequency of array elements

Question

In Javascript, I\'m trying to take an initial array of number values and count the elements inside it. Ideally, the result would be two new arrays, the first specifying each

Answer 1

Here you go:

Live demo: http://jsfiddle.net/simevidas/bnACW/

Note

This changes the order of the original input array using Array.sort

var arr = [2, 2, 2, 2, 2, 4, 5, 5, 5, 9];

function foo(arr) {
  var a = [],
    b = [],
    prev;

  arr.sort();
  for (var i = 0; i < arr.length; i++) {
    if (arr[i] !== prev) {
      a.push(arr[i]);
      b.push(1);
    } else {
      b[b.length - 1]++;
    }
    prev = arr[i];
  }

  return [a, b];
}

var result = foo(arr);
console.log('[' + result[0] + ']','[' + result[1] + ']')