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

You can use an object to hold the results:

var arr = [5, 5, 5, 2, 2, 2, 2, 2, 9, 4];
var counts = {};

for (var i = 0; i < arr.length; i++) {
  var num = arr[i];
  counts[num] = counts[num] ? counts[num] + 1 : 1;
}

console.log(counts[5], counts[2], counts[9], counts[4]);

So, now your counts object can tell you what the count is for a particular number:

console.log(counts[5]); // logs '3'

If you want to get an array of members, just use the keys() functions

keys(counts); // returns ["5", "2", "9", "4"]