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POWhat is the most efficient way to implement GroupBy in Javascript?
 

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  1. POWhat is the most efficient way to implement GroupBy in Javascript?
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    <p>I am trying to implement a <code>GroupBy</code> method with these parameters</p> <pre><code>function GroupBy(keySelector, elementSelector, comparer) { // keySelector = function(e) { return e.ID } // elementSelector = function(e) { return e.Name } // comparer = { Equals: function(a,b) { return a==b }, GetHashCode:... } } </code></pre> <p>However I don't know an efficient way to implement it.</p> <p><a href="http://jsperf.com/js-groupby-complex" rel="noreferrer">I created a jsPerf test</a> with linq.js and a method I created which doesn't use a comparer and only work on flat types. (<a href="http://jsfiddle.net/BDQ4k/" rel="noreferrer">Output test here</a>)</p> <p>Other libraries such as underscore and Lo-Dash doesn't take a <code>comparer</code> parameter. So their implementations are irrelevant.</p> <p>My key could be a class, so I need something to determine if <code>TKey</code> is the same in different instances.</p> <p>So basically what I am trying to do is copy C# Linq <code>GroupBy</code> behavior <a href="http://msdn.microsoft.com/en-us/library/bb534304%28v=vs.110%29.aspx" rel="noreferrer">documented here</a>.</p> <p>Sample input:</p> <pre><code>var arrComplex = [ { N: { Value: 10 }, Name: "Foo" }, { N: { Value: 10 }, Name: "Bar" }, { N: { Value: 20 }, Name: "Foo" }, { N: { Value: 20 }, Name: "Bar" } ]; </code></pre> <p>Sample output (or something like this):</p> <pre><code>[ { "Key": {"Value":10}, "Elements":["Foo","Bar"] }, { "Key": {"Value":20}, "Elements":["Foo","Bar"] } ] </code></pre> <p>Any ideas on how to implement it?</p> <h3>Bounty</h3> <p>For the bounty I would like you take in consideration that:</p> <ul> <li>The key could be an object</li> <li>Two objects can be equal if some property is equal</li> <li>It should be as fast as or faster than existing solutions</li> <li>The result can be an array or object, doesn't matter as long as I can get elements grouped by a key</li> </ul> <p>Well, I expect a complete answer.</p>
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    1. CODo you really need your own implementation? Can't you use `Underscore.js` or other library?
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    2. CO`Lo-Dash.js` is another alternative and it bills itself as faster and more efficient than `Underscore.js`
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    3. COBoth doesn't seem to have a `comparer` parameter.
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