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    <p>Unfortunately there is no built-in inverse of array_combine. There is also no way to define one, since array_combine expects multiple parameters and we can't return multiple values from a function.</p> <p>We can construct an alternative to array_combine which takes a single argument: the array of keys and the array of values wrapped up together in another array. This transformation is called "uncurrying" and is performed by the "call_user_func_array" function:</p> <pre><code>$array_comb = function($arr) { return call_user_func_array('array_combine', $arr); }; </code></pre> <p>This alternative function does have an inverse:</p> <pre><code>$array_split = function($arr) { return array(array_keys($arr), array_values($arr)); }; </code></pre> <p>If we define function composition:</p> <pre><code>$compose = function($f, $g) { return function($x) use ($f, $g) { return $f($g($x)); }; }; </code></pre> <p>Then the following functions are all (extensionally) equal, ie. they all return their argument unchanged:</p> <pre><code>$identity = function($x) { return $x; }; $left_inverse = $compose($array_split, $array_comb); // Split then combine $right_inverse = $compose($array_comb, $array_split); // Combine then split </code></pre> <p>Note that they accept different argument types though:</p> <ul> <li>$identity will work on anything.</li> <li>$left_inverse will work on any array.</li> <li>$right_inverse will work on arrays-of-arrays, where the outer array contains 2 elements, both inner arrays are of equal length and the first inner array only contains integers and strings.</li> </ul>
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    1. POPHP Splitting an Array into two arrays - keys array and values array
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