array_walk_recursive

(PHP 5, PHP 7)

array_walk_recursive — Apply a user function recursively to every member of an array

Description

bool array_walk_recursive ( array &$array , callable $callback [, mixed $userdata = NULL ] )

Applies the user-defined callback function to each element of the array. This function will recurse into deeper arrays.

Parameters

array: The input array.
callback: Typically, callback takes on two parameters. The array parameter's value being the first, and the key/index second.

Note:
If callback needs to be working with the actual values of the array, specify the first parameter of callback as a reference. Then, any changes made to those elements will be made in the original array itself.
userdata: If the optional userdata parameter is supplied, it will be passed as the third parameter to the callback.

Return Values

Returns TRUE on success or FALSE on failure.

Examples

Example #1 array_walk_recursive() example


<?php
$sweet = array('a' => 'apple', 'b' => 'banana');
$fruits = array('sweet' => $sweet, 'sour' => 'lemon');

function test_print($item, $key)
{
    echo "$key holds $item\n";
}

array_walk_recursive($fruits, 'test_print');
?>

The above example will output:

a holds apple
b holds banana
sour holds lemon

You may notice that the key 'sweet' is never displayed. Any key that holds an array will not be passed to the function.

User Contributed Notes

none at of dot your dot biz

2 years ago


Since this is only mentioned in the footnote of the output of one of the examples, I feel it should be spelled out:

* THIS FUNCTION ONLY VISITS LEAF NODES *

That is to say that if you have a tree of arrays with subarrays of subarrays, only the plain values at the leaves of the tree will be visited by the callback function.  The callback function isn't ever called for a nodes in the tree that subnodes (i.e., a subarray).  This has the effect as to make this function unusable for most practical situations.

gk at anuary dot com

2 years ago


array_walk_recursive itself cannot unset values. Even though you can pass array by reference, unsetting the value in the callback will only unset the variable in that scope.



<?php

/**

 * http://uk1.php.net/array_walk_recursive implementation that is used to remove nodes from the array.

 *

 * @param array The input array.

 * @param callable $callback Function must return boolean value indicating whether to remove the node.

 * @return array

 */

function walk_recursive_remove (array $array, callable $callback) {

    foreach ($array as $k => $v) {

        if (is_array($v)) {

            $array[$k] = walk_recursive_remove($v, $callback);

        } else {

            if ($callback($v, $k)) {

                unset($array[$k]);

            }

        }

    }



    return $array;

}

?>



An up to date implementation of the above function can be looked up from https://github.com/gajus/marray/blob/master/src/marray.php#L116.

ghoffman at salientdigital dot com

4 years ago


If you are wanting to change the values of an existing multi-dimensional array, as it says above in the note, you need to specify the first argument as a reference. All that means is, be sure to precede the $item variable with an ampersand (&) as in the good_example below. 

Unfortunately the PHP example given doesn't do this. It actually took me a while to figure out why my function wasn't changing the original array, even though I was passing by reference. 

Here's the tip: Don't return any value from the function! Just change the value of $item that you passed in by reference. This is rather counter-intuitive since the vast majority of functions return a value.

<?php
// array_walk_recursive fails to change your array unless you pass by reference.
// Don't return values from your filter function, even though it's quite logical at a glance!
function bad_example($item,$key){
   if($key=='test'){
       return 'PHP Rocks';  // Don't do it
   }else{
      return $item;  // Don't do this either
   }
}

// array_walk_recursive pass-by-reference example
function good_example(&$item,$key){
   if($key=='test'){
        $item='PHP Rocks'; // Do This!
   }
}

$arr = array('a'=>'1','b'=>'2','test'=>'Replace This');

array_walk_recursive($arr,'bad_example');
var_dump($arr);
/**
 * no errors, but prints...
 * array('a'=>'1','b'=>'2','test'=>'Replace This');
 */

array_walk_recursive($arr,'good_example');
var_dump($arr);
/**
 * prints...
 * array('a'=>'1','b'=>'2','test'=>'PHP Rocks');
 */

?>

Returning a value from your function does work if you pass by reference and modify $item before you return, but you will eat up memory very, very fast if you try it, even on an example as small as the one here.

One other silly thing you might try first is something like this:

<?php
// Resist the urge to do this, it doesn't work.
$filtered = array_walk_recursive($unfiltered,'filter_function');
?>

Of course, $filtered is just TRUE afterwards, not the filtered results you were wanting. Oh, it ran your function recursively alright, but changed all the values in the local function scope only and returns a boolean as the documentation states.

bradbeattie at gmail dot com

5 years ago


The description says "If funcname needs to be working with the actual values of the array, specify the first parameter of funcname as a reference." This isn't necessarily helpful as the function you're calling might be built in (e.g. trim or strip_tags). One option would be to create a version of these like so.



<?php

    function trim_by_reference(&$string) {

        $string = trim($string);

    }

?>



The downside to this approach is that you need to create a wrapper function for each function you might want to call. Instead, we can use PHP 5.3's inline function syntax to create a new version of array_walk_recursive.



<?php

    /**

     * This function acts exactly like array_walk_recursive, except that it pretends that the function

     * its calling replaces the value with its result.

     * 

     * @param $array The first value of the array will be passed into $function as the primary argument

     * @param $function The function to be called on each element in the array, recursively

     * @param $parameters An optional array of the additional parameters to be appeneded to the function

     * 

     * Example usage to alter $array to get the second, third and fourth character from each value

     *     array_walk_recursive_referential($array, "substr", array("1","3"));

     */

    function array_walk_recursive_referential(&$array, $function, $parameters = array()) {

        $reference_function = function(&$value, $key, $userdata) {

            $parameters = array_merge(array($value), $userdata[1]);

            $value = call_user_func_array($userdata[0], $parameters);

        };

        array_walk_recursive($array, $reference_function, array($function, $parameters));

    }

?>



The advantage here is that we only explicitly define one wrapper function instead of potentially dozens.

robin leffmann

1 year ago


A simple solution for walking a nested array to obtain the last set value of a specified key:

<?php

$key = 'blah';
$val = null;
array_walk_recursive( $your_array,
                      function($v, $k, $u) { if($k === $u[0]) $u[1] = $v; },
                      [$key ,&$val] );

echo "$key = $val";

?>

php at genjo dot fr

1 year ago


I use RecursiveIteratorIterator with parameter CATCH_GET_CHILD to iterate on leafs AND nodes instead of array_walk_recursive function :

<?php
// Iteration on leafs AND nodes
foreach (new RecursiveIteratorIterator(new RecursiveArrayIterator($candidate), RecursiveIteratorIterator::CATCH_GET_CHILD) as $key => $value) {
    echo 'My node ' . $key . ' with value ' . $value . PHP_EOL;
}
?>

Anonymous

2 years ago


since PHP 5.3.0, you will get a warning saying that "call-time pass-by-reference" is deprecated when you use & in foo(&$a);. And as of PHP 5.4.0, call-time pass-by-reference was removed, so using it will raise a fatal error.

cyranix at cyranix dot com

4 years ago


I needed to add or modify values in an array with unknown structure. I was hoping to use array_walk_recursive for the task, but because I was also adding new nodes I came up with an alternate solution.

<?php

    /**
     * Sets key/value pairs at any depth on an array.
     * @param $data an array of key/value pairs to be added/modified
     * @param $array the array to operate on
     */
    function setNodes($data, &$array)
    {
        $separator = '.'; // set this to any string that won't occur in your keys
        foreach ($data as $name => $value) {
            if (strpos($name, $separator) === false) {
                // If the array doesn't contain a special separator character, just set the key/value pair. 
                // If $value is an array, you will of course set nested key/value pairs just fine.
                $array[$name] = $value;
            } else {
                // In this case we're trying to target a specific nested node without overwriting any other siblings/ancestors. 
                // The node or its ancestors may not exist yet.
                $keys = explode($separator, $name);
                // Set the root of the tree.
                $opt_tree =& $array;
                // Start traversing the tree using the specified keys.
                while ($key = array_shift($keys)) {
                    // If there are more keys after the current one...
                    if ($keys) {
                        if (!isset($opt_tree[$key]) || !is_array($opt_tree[$key])) {
                            // Create this node if it doesn't already exist.
                            $opt_tree[$key] = array();
                        }
                        // Redefine the "root" of the tree to this node (assign by reference) then process the next key.
                        $opt_tree =& $opt_tree[$key];
                    } else {
                        // This is the last key to check, so assign the value.
                        $opt_tree[$key] = $value;
                    }
                }
            }
        }
    }

?>

Sample usage: 

<?php

$x = array();
setNodes(array('foo' => 'bar', 'baz' => array('quux' => 42, 'hup' => 101)), $x);
print_r($x); // $x has the same structure as the first argument
setNodes(array('jif.snee' => 'hello world', 'baz.quux.wek' => 5), $x);
print_r($x); // added $x['jif']['snee'] and modified $x['baz']['quux'] to be array('wek' => 5)

?>

Rodrigo Guariento

2 years ago


Simple array_walk_recursive:

// var example
$myArray = Array(
  Array('keyA1' => '    textA1 ', 'keyA2' => '  textA2     '),
  Array('keyB1' => '    textB1 ', 'sub' => 
        Array('keyB1_sub1' => '      textB1_sub1   '),
          Array('keyB1_sub2' => '      textB1_sub2   ')
      ),
  Array('keyC1' => '    textC1 ', 'keyC2' => '  textC2     '),
  Array('keyD1' => '    textD1 ', 'keyD2' => '  textD2     '),
  Array('keyE1' => '    textE1 ', 'keyE2' => '  textE2     ')
);

// function for "trim" (or your function, use same structure)
function trimming($data) {
  if (gettype($data) == 'array')
    return array_map("trimming", $data);
  else
    return trim($data);
}

// get array
$myArray = array_map("trimming", $myArray);

// show array trimmed
var_dump($myArray);

/*
RESULT

array (size=5)
  0 => 
    array (size=2)
      'keyA1' => string 'textA1' (length=6)
      'keyA2' => string 'textA2' (length=6)
  1 => 
    array (size=3)
      'keyB1' => string 'textB1' (length=6)
      'sub' => 
        array (size=1)
          'keyB1_sub1' => string 'textB1_sub1' (length=11)
      0 => 
        array (size=1)
          'keyB1_sub2' => string 'textB1_sub2' (length=11)
  2 => 
    array (size=2)
      'keyC1' => string 'textC1' (length=6)
      'keyC2' => string 'textC2' (length=6)
  3 => 
    array (size=2)
      'keyD1' => string 'textD1' (length=6)
      'keyD2' => string 'textD2' (length=6)
  4 => 
    array (size=2)
      'keyE1' => string 'textE1' (length=6)
      'keyE2' => string 'textE2' (length=6)

*/

chris at willowsconsulting dot ie

3 years ago


To convert all values of an array in UTF8, do this:

<?php

function convert_before_json(&$item, &$key)
{
   $item=utf8_encode($item);
}

array_walk_recursive($your_array,"convert_before_json");

?>

amoffat at amoffat dot com

7 years ago


<?
function my_array_map() {
    $args = func_get_args();
    $arr = array_shift($args);
    
    foreach ($args as $fn) {
        $nfn = create_function('&$v, $k, $fn', '$v = $fn($v);');
        array_walk_recursive($arr, $nfn, $fn);
    }
    return $arr;
}
?>

takes an array as the first argument, and functions as the other arguments.  it applies those functions recursively to the array

8 years ago


This function has a serious bug, which is still not fixed as of the PHP 5.2.5 release. After you call it, it can accidentally modify your original array. Save yourself hours of frustration by reading on.

The bug is here: http://bugs.php.net/bug.php?id=42850, and it looks like it will be fixed for 5.3.

If the array that you walk contains other array elements, they will be turned into references. This will happen even if the callback function doesn't take its first argument by reference, and doesn't do anything to the values.

For example, try this:
<?php
$data = array ('key1' => 'val1', 'key2' => array('key3' => 'val3'));
function foo($item, $key){}
var_dump($data);
?>

The original array has no references. Now try this:
<?php
array_walk_recursive($data,'foo');
var_dump($data);
?>

Now key2 is a reference, not just an array. So if you do this:
<?php
function test($item){$item['key2'] = array();}
test($data);
var_dump($data);
?>

you will see that test modifies $data, even though it shouldn't.

One workaround is to immediately make a deep copy of the array after calling array_walk_recursive, like this:
<?php
function array_duplicate($input) {
  if (!is_array($input)) return $input;
  $output = array();
  foreach ($input as $key => $value) {
    $output[$key] = array_duplicate($value);
  }
  return $output;
}
array_walk_recursive($data,'foo');
$data = array_duplicate($data);
var_dump($data);
?>

After doing that, the references are gone.

gabrielu at hotmail dot com

10 years ago


I decided to add to the previous PHP 4 compatible version of array_walk_recursive() so that it would work within a class and as a standalone function.  Both instances are handled by the following function which I modified from omega13a at sbcglobal dot net.

The following example is for usage within a class.  To use as a standalone function take it out of the class and rename it.  (Example: array_walk_recursive_2)

<?php
class A_Class {

function array_walk_recursive(&$input, $funcname, $userdata = '') {
  if(!function_exists('array_walk_recursive')) {
    if(!is_callable($funcname))
      return false;

    if(!is_array($input))
      return false;

    foreach($input as $key=>$value) {
      if(is_array($input[$key])) {
        if(isset($this)) {
          eval('$this->' . __FUNCTION__ . '($input[$key], $funcname, $userdata);');
        } else {
          if(@get_class($this))
            eval(get_class() . '::' . __FUNCTION__ . '($input[$key], $funcname, $userdata);');
          else
            eval(__FUNCTION__ . '($input[$key], $funcname, $userdata);');
        }
      } else {
        $saved_value = $value;

        if(is_array($funcname)) {
          $f = '';
          for($a=0; $a<count($funcname); $a++)
            if(is_object($funcname[$a])) {
              $f .= get_class($funcname[$a]);
            } else {
              if($a > 0)
                $f .= '::';
              $f .= $funcname[$a];
            }
          $f .= '($value, $key' . (!empty($userdata) ? ', $userdata' : '') . ');';
          eval($f);
        } else {
          if(!empty($userdata))
            $funcname($value, $key, $userdata);
          else
            $funcname($value, $key);
        }

        if($value != $saved_value)
          $input[$key] = $value;
      }
    }
    return true;
  } else {
    array_walk_recursive($input, $funcname, $userdata);
  }
}

function kv_addslashes(&$v, $k) {
  $v = addslashes($v);
}
}
?>

Usage:
<?php
$arr = array(
  'a' => '"Hello World"',
  'b' => "'Hello World'",
  'c' => "Hello 'Worl\"d",
  'd' => array(
    'A' => 'H"e"l"l"o" "W"o"r"l"d'
    )
  );

$class = new A_Class();
$class->array_walk_recursive($arr, array(&$class, 'kv_addslashes'));
print_r($arr);
?>

rob at yurkowski dot net

5 years ago


If you don't really particularly care about the keys of an array, you can capture all values quite simply:



<?php



$sample = array('dog' => 'woof', 'cat' => array('angry' => 'hiss', 'happy' => 'purr'), 'aardvark' => 'kssksskss');

$output = array();



// Push all $val onto $output.

array_walk_recursive($sample, create_function('$val, $key, $obj', 'array_push($obj, $val);'), &output);



// Printing

echo nl2br(print_r($output, true));



/* 

* Array

* (

*  [0] => woof

*  [1] => hiss

*  [2] => purr

*  [3] => kssksskss

* )

*/

?>



[EDIT BY danbrown AT php DOT net: In a note added by 'FaustoFilho' on 17-MAY-2011, the following information was appended to this note.



[If you intend to use this] "function to extract the last key value of an array, don't forget to insert a currency sign ($) signal before '$output' at 7th line.



This value must be a variable, and if you forgot to assign this signal, your code won't work, displaying an error like this:



Parse error: syntax error, unexpected ')', expecting T_PAAMAYIM_NEKUDOTAYIM in /path/to/script.php on line 7."]

ik at paulkaspers dot nl

9 years ago


To egingell at sisna dot com:

There is a small bug in your function, the following line should be changed:
From: if ($value != $saved_value || $saved_key != $key) {
Into: if ($value !== $saved_value || $saved_key !== $key) {

It's a nice function, because I was searching for something to change the keys of a multiple dimension array.

omega13a at sbcglobal dot net

10 years ago


This is a peice of code I wrote that appears to create this function for PHP 4.

<?php
if (!function_exists('array_walk_recursive'))
{
    function array_walk_recursive(&$input, $funcname, $userdata = "")
    {
        if (!is_callable($funcname))
        {
            return false;
        }
        
        if (!is_array($input))
        {
            return false;
        }
        
        foreach ($input AS $key => $value)
        {
            if (is_array($input[$key]))
            {
                array_walk_recursive($input[$key], $funcname, $userdata);
            }
            else
            {
                $saved_value = $value;
                if (!empty($userdata))
                {
                    $funcname($value, $key, $userdata);
                }
                else
                {
                    $funcname($value, $key);
                }
                
                if ($value != $saved_value)
                {
                    $input[$key] = $value;
                }
            }
        }
        return true;
    }
}
?>

Please note it is a conditionaly set function and will have to be put before any call to it.

If there is anything wrong with it, please email me.

array_walk_recursive

Description

Parameters

Return Values

Examples

See Also

User Contributed Notes