Underscore.js Collections: GroupBy

HTML

<script src="http://documentcloud.github.com/underscore/underscore-min.js"></script>
<a target="parent" href="http://underscorejs.org/#groupBy">Learn More</a>

<script src="https://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.9.1/underscore-min.js"></script>

JavaScript

var arr = [1.3, 2.1, 2.4],
arr2 = ['one', 'two', 'three'];

var testGroupBy = _.groupBy(arr, function(num){ return Math.floor(num); });

console.log(testGroupBy[1],testGroupBy[2]);
//[1.3] [2.1, 2.4] 

//Math.Floor(1.3) = 1;
// So 1.3 is in group 1;

var testGroupBy2 = _.groupBy(arr2, 'length');

console.log(testGroupBy2[3],testGroupBy2[5]);
//["one", "two"] ["three"] 

// One & Two have 3 letters so they are in group 3, 
// Three has 5 letters so it's in group 5