array_map

Let's assume we have following situation:<?phpclass MyFilterClass {    public function filter(array $arr) {        return array_map(function($value) {            return $this->privateFilterMethod($value);        });    }    private function privateFilterMethod($value) {        if (is_numeric($value)) $value++;        else $value .= '.';    }}?>This will work, because $this inside anonymous function (unlike for example javascript) is the instance of MyFilterClass inside which we called it.I hope this would be useful for anyone.

To transpose rectangular two-dimension array, use the following code:array_unshift($array, null);$array = call_user_func_array("array_map", $array);If you need to rotate rectangular two-dimension array on 90 degree, add the following line before or after (depending on the rotation direction you need) the code above:$array = array_reverse($array);Here is example:<?php$a = array(  array(1, 2, 3),  array(4, 5, 6));array_unshift($a, null);$a = call_user_func_array("array_map", $a);print_r($a);?>Output:Array(    [0] => Array        (            [0] => 1            [1] => 4        )    [1] => Array        (            [0] => 2            [1] => 5        )    [2] => Array        (            [0] => 3            [1] => 6        ))

If the callback function to be called is a static method from a different namespace, the fully qualified method including namespace must be specified (a use statement is not sufficient to resolve the namespace of the callback function)<?phpuse MyTools;$arr = [1, 2, 3];$arr = array_map('Tools::myHelper', $arr);?>will cause TypeError: array_map() expects parameter 1 to be a valid callback, class 'Tools' not found.Use the fully qualified name for the callback instead:<?php$arr = [1, 2, 3];$arr = array_map('\MyTools\Tools::myHelper', $arr);?>

You may be looking for a method to extract values of a multidimensional array on a conditional basis (i.e. a mixture between array_map and array_filter) other than a for/foreach loop. If so, you can take advantage of the fact that 1) the callback method on array_map returns null if no explicit return value is specified (as with everything else) and 2) array_filter with no arguments removes falsy values. So for example, provided you have:<?php$data = [    [        "name" => "John",        "smoker" => false    ],    [        "name" => "Mary",        "smoker" => true    ],    [        "name" => "Peter",        "smoker" => false    ],    [        "name" => "Tony",        "smoker" => true    ]];?>You can extract the names of all the non-smokers with the following one-liner:<?php$names = array_filter(array_map(function($n) { if(!$n['smoker']) return $n['name']; }, $data));?>It's not necessarily better than a for/foreach loop, but the occasional one-liner for trivial tasks can help keep your code cleaner.

The most memory-efficient array_map_recursive().<?phpfunction array_map_recursive(callable $func, array $arr) {    array_walk_recursive($arr, function(&$v) use ($func) {        $v = $func($v);    });    return $arr;}?>

A general solution for the problem of wanting to know the keys in the callback, and/or retain the key association in the returned array:<?php/** * Like array_map() but callback also gets passed the current key as the * first argument like so: * function($key, $val, ...$vals) { ... } * ...and returned array always maintains key association, even if multiple * array arguments are passed. */function array_map_assoc(callable $callback, array $array, array ...$arrays) {    $keys = array_keys($array);    array_unshift($arrays, $keys, $array);    return array_combine($keys, array_map($callback, ...$arrays));}?>Because it uses array_map() directly, it behaves the same way in regard to ignoring the keys of subsequent array arguments. It also has the same variadic signature.

If you want to pass an argument like ENT_QUOTES to htmlentities, you can do the follow.<?php$array = array_map( 'htmlentities' , $array, array_fill(0 , count($array) , ENT_QUOTES) );?>The third argument creates an equal sized array of $array filled with the parameter you want to give with your callback function.

/**   * Function which recursively applies a callback to all values and also its  * keys, and returns the resulting array copy with the updated keys and   * values.  * PHP's built-in function array_walk_recursive() only applies the passed   * callback to the array values, not the keys, so this function simply applies  * the callback to the keys too (hence the need of working with a copy,   * as also updating the keys would lead to reference loss of the original  * array). I needed something like this, hence my idea of sharing it here.  *  * @param    callable    $func     callback which takes one parameter (value   *                                                   or key to be updated) and returns its   *                                                   updated value  *  * @param    array          $arr      array of which keys and values shall be   *                                                   get updated   */function array_map_recursive(    callable $func,    array $arr) {      // Initiate copied array which will hold all updated keys + values      $result = [];      // Iterate through the key-value pairs of the array      foreach ( $arr as $key => $value ) {        // Apply the callback to the key to create the updated key value        $updated_key = $func( $key );        // If the iterated value is not an array, that means we have reached the        // deepest array level for the iterated key, so in that case, assign        // the updated value to the updated key value in the final output array        if ( ! is_array( $value ) ) {          $result[$updated_key] = $func( $value );        } else {          // If the iterated value is an array, call the function recursively,          // By taking the currently iterated value as the $arr argument          $result[$updated_key] = array_map_recursive(            $func,            $arr[$key]          );        }      } // end of iteration through k-v pairs      // And at the very end, return the generated result set      return $result;    } // end of array_map_recursive() function definition