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POUnwanted behavior of PHP usort
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  1. POUnwanted behavior of PHP usort
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    copied!<p>I have a problem with PHP <code>usort()</code>. Let's suppose I have an array like this (that's a simplification, I've not to work with names, and I have an array of objects, not arrays):</p> <pre><code>$data = array( array('name' =&gt; 'Albert', 'last' =&gt; 'Einstein'), array('name' =&gt; 'Lieserl', 'last' =&gt; 'Einstein'), array('name' =&gt; 'Alan', 'last' =&gt; 'Turing' ), array('name' =&gt; 'Mileva', 'last' =&gt; 'Einstein'), array('name' =&gt; 'Hans Albert', 'last' =&gt; 'Einstein') ); </code></pre> <p>As you can see, the array is sorted arbitrarily.</p> <p>Now, if want to sort it by <code>last</code>, I do:</p> <pre><code>function sort_some_people($a, $b) { return strcmp($a['last'], $b['last']); } usort($data, 'sort_some_people'); </code></pre> <p>And I have:</p> <pre><code>Array ( [0] =&gt; Array ( [name] =&gt; Mileva [last] =&gt; Einstein ) [3] =&gt; Array ( [name] =&gt; Albert [last] =&gt; Einstein ) [1] =&gt; Array ( [name] =&gt; Lieserl [last] =&gt; Einstein ) [2] =&gt; Array ( [name] =&gt; Hans Albert [last] =&gt; Einstein ) [4] =&gt; Array ( [name] =&gt; Alan [last] =&gt; Turing ) ) </code></pre> <p>That is ok, now they are sorted by <code>last</code>. But, as you can see, I've just completely lost the previous sorting. What am I saying? I want to preserve array sorting as it was before, but as a <em>secondary</em> sorting. I hope I was clear. <strong>Practically</strong> I want to sort data using something as <code>usort()</code> (so, a completely custom sorting), but if sorting field is identical between two items, I want to keep their <em>relative position</em> as it was before. Considering the given example, I want <code>Lieserl Einstein</code> to appear before <code>Mileva Einstein</code> because it was like this at beginning.</p>
 

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