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

Don't use two arrays for the result, use an object:

a      = [5, 5, 5, 2, 2, 2, 2, 2, 9, 4];
result = { };
for(var i = 0; i < a.length; ++i) {
    if(!result[a[i]])
        result[a[i]] = 0;
    ++result[a[i]];
}

Then result will look like:

{
    2: 5,
    4: 1,
    5: 3,
    9: 1
}