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    copied!<p>The sorting algorithms used in PHP have this property where the order is undefined if the items match.</p> <p>If you need to keep the order, then you have to roll your own code.</p> <p>Fortunately some one already has: <a href="http://www.php.net/manual/en/function.usort.php#38827" rel="nofollow">http://www.php.net/manual/en/function.usort.php#38827</a></p> <pre><code>$data = array( array('name' =&gt; 'Albert', 'last' =&gt; 'Einstein'), array('name' =&gt; 'Lieserl', 'last' =&gt; 'Einstein'), array('name' =&gt; 'Alan', 'last' =&gt; 'Turing' ), array('name' =&gt; 'Mileva', 'last' =&gt; 'Einstein'), array('name' =&gt; 'Hans Albert', 'last' =&gt; 'Einstein') ); function sort_some_people($a, $b) { return strcmp($a['last'], $b['last']); } function mergesort(&amp;$array, $cmp_function = 'strcmp') { // Arrays of size &lt; 2 require no action. if (count($array) &lt; 2) return; // Split the array in half $halfway = count($array) / 2; $array1 = array_slice($array, 0, $halfway); $array2 = array_slice($array, $halfway); // Recurse to sort the two halves mergesort($array1, $cmp_function); mergesort($array2, $cmp_function); // If all of $array1 is &lt;= all of $array2, just append them. if (call_user_func($cmp_function, end($array1), $array2[0]) &lt; 1) { $array = array_merge($array1, $array2); return; } // Merge the two sorted arrays into a single sorted array $array = array(); $ptr1 = $ptr2 = 0; while ($ptr1 &lt; count($array1) &amp;&amp; $ptr2 &lt; count($array2)) { if (call_user_func($cmp_function, $array1[$ptr1], $array2[$ptr2]) &lt; 1) { $array[] = $array1[$ptr1++]; } else { $array[] = $array2[$ptr2++]; } } // Merge the remainder while ($ptr1 &lt; count($array1)) $array[] = $array1[$ptr1++]; while ($ptr2 &lt; count($array2)) $array[] = $array2[$ptr2++]; return; } mergesort($data, 'sort_some_people'); print_r($data); </code></pre> <p>Output:</p> <pre><code>Array ( [0] =&gt; Array ( [name] =&gt; Albert [last] =&gt; Einstein ) [1] =&gt; Array ( [name] =&gt; Lieserl [last] =&gt; Einstein ) [2] =&gt; Array ( [name] =&gt; Mileva [last] =&gt; Einstein ) [3] =&gt; Array ( [name] =&gt; Hans Albert [last] =&gt; Einstein ) [4] =&gt; Array ( [name] =&gt; Alan [last] =&gt; Turing ) ) </code></pre> <p>Voila! </p>
 

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