Condensing a sparse array in Javascript?

Question

I have an array of elements where the entries are sparse. How can I easily condense the sparse array into a dense array so that I don\'t have to keep checking for null and

Answer 1

You can use filter() which is compatible with Firefox, Chrome, IE 9, Opera, and Safari web browsers.

According to David Flanagan, in Javascript: The Definitive Guide, an easy way of transforming a sparse array to a dense array is to use a filter on it like so:

var dense = sparse.filter(function (x) { return x !== undefined && x != null; });

This works since filter() skips missing elements and only returns true if x is not undefined or null.

If filter() is not supported, this will compact a sparse array:

var compacted = [];

for(var i = 0; i < sparse.length; i++)
    if(i in sparse)
        compacted.push(sparse[i]);

An exact equivalent of the filter() example is:

var compacted = [];

for(var i = 0; i < sparse.length; i++)
    if(sparse[i] != null)
        compacted.push(sparse[i]);