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

If you are using underscore you can go the functional route

a = ['foo', 'foo', 'bar'];

var results = _.reduce(a,function(counts,key){ counts[key]++; return counts },
                  _.object( _.map( _.uniq(a), function(key) { return [key, 0] })))

so your first array is

_.keys(results)

and the second array is

_.values(results)

most of this will default to native javascript functions if they are available

demo : http://jsfiddle.net/dAaUU/