iterate over an object retrieved from _.groupBy

Question

With the underscore function groupBy, an array can be grouped by one of its element's properties. The result is an object which has key-value pairs as followed: group > corresponding array fragment.

var words = ['Hey', 'Hii', 'Salut'],
    grouped = _.groupBy(words, 'length');

grouped looks like this:

{
  '3': ['Hey', 'Hii'],
  '5': ['Salut']
}

Which would be a simple and secure way to iterate over this, say starting with the highest length followed by the next lowest. This works:

_.each( _.toArray(grouped).reverse(), function(v) {
  console.log(v);
} );

But I think it's not totally correct, because objects are unordered lists, and the right order happens here just by chance. Any comments on this?

Answer 1

You are right in that you cannot rely on the object keys sorting, you need to enforce the right sorting. With underscore you can use _.sortBy:

_.each(
    _.sortBy(
        _.toArray(grouped), function (num) {
            return num;
        }
    ).reverse(),
    function (v) {
        console.log(v);
    }
);