The array_diff_assoc_array from "chinello at gmail dot com" (and others) will not work for arrays with null values. That's because !isset is true when an array key doesn't exists or is set to null.

(sorry for the changed indent-style)
<?php
function array_diff_assoc_recursive($array1, $array2) {
    $difference=array();
    foreach($array1 as $key => $value) {
        if( is_array($value) ) {
            if( !isset($array2[$key]) || !is_array($array2[$key]) ) {
                $difference[$key] = $value;
            } else {
                $new_diff = array_diff_assoc_recursive($value, $array2[$key]);
                if( !empty($new_diff) )
                    $difference[$key] = $new_diff;
            }
        } else if( !array_key_exists($key,$array2) || $array2[$key] !== $value ) {
            $difference[$key] = $value;
        }
    }
    return $difference;
}
?>

And here an example (note index 'b' in the output):
<?php
$a1=array( 'a' => 0, 'b' => null, 'c' => array( 'd' => null ) );
$a2=array( 'a' => 0, 'b' => null );

var_dump( array_diff_assoc_recursive( $a1, $a2 ) );
var_dump( chinello_array_diff_assoc_recursive( $a1, $a2 ) );
?>
array(1) {
  ["c"]=>
  array(1) {
    ["d"]=>
    NULL
  }
}

array(2) {
  ["b"]=>
  NULL
  ["c"]=>
  array(1) {
    ["d"]=>
    NULL
  }
}

The direction of the arguments does actually make a difference:

<?php
$a = array(
    'x' => 'x',
    'y' => 'y',
    'z' => 'z',
    't' => 't',
);

$b = array(
    'x' => 'x',
    'y' => 'y',
    'z' => 'z',
    't' => 't',
    'g' => 'g',
);

print_r(array_diff_assoc($a, $b));
print_r(array_diff_assoc($b, $a));
?>

echoes:

Array
(
)
Array
(
    [g] => g
)

If you're looking for a true array_diff_assoc, comparing arrays to determine the difference between two, finding missing values from both, you can use this along with array_merge.

$a = array('a'=>1,'b'=>2,'c'=>3);
$b = array('a'=>1,'b'=>2,'d'=>4);
print_r(array_diff_assoc($a,$b));
// returns:
array
(
    [c] => 3
)

print_r(array_diff_assoc($b,$a));
// returns 
array
(
    [d] => 4
)

print_r(array_merge(array_diff_assoc($a,$b),array_diff_assoc($b,$a)));
// returns
array
(
    [c] => 3
    [d] => 4
)

an earlier post for recursive array_diff_assoc failed because isset returned false on an array element containing a null value. I updated the code so it compares null values too.

<?php 
function array_diff_assoc_recursive($array1, $array2) 
{ 
    foreach($array1 as $key => $value) 
    { 
        if(is_array($value)) 
        { 
              if(!isset($array2[$key])) 
              { 
                  $difference[$key] = $value; 
              } 
              elseif(!is_array($array2[$key])) 
              { 
                  $difference[$key] = $value; 
              } 
              else 
              { 
                  $new_diff = array_diff_assoc_recursive($value, $array2[$key]); 
                  if($new_diff != FALSE) 
                  { 
                        $difference[$key] = $new_diff; 
                  } 
              } 
          } 
          elseif(!array_key_exists($key, $array2) || $array2[$key] != $value) 
          { 
              $difference[$key] = $value; 
          } 
    } 
    return !isset($difference) ? 0 : $difference; 
} 
?>

Works more like the original function:

<?php

function array_diff_assoc_recursive ( )
{
    $args = func_get_args ( );
    $diff = array ( );
    foreach ( array_shift ( $args ) as $key => $val )
    {
        for ( $i = 0, $j = 0, $tmp = array ( $val ) , $count = count ( $args ); $i < $count; $i++ )
            if ( is_array ( $val ) )
                if ( !isset ( $args[$i][$key] ) || !is_array ( $args[$i][$key] ) || empty( $args[$i][$key] ) )
                    $j++;
                else
                    $tmp[] = $args[$i][$key];
            elseif ( ! array_key_exists ( $key, $args[$i] ) || $args[$i][$key] !== $val )
                $j++;
        if ( is_array ( $val ) )
        {
            $tmp = call_user_func_array ( __FUNCTION__, $tmp );
            if ( ! empty ( $tmp ) ) $diff[$key] = $tmp;
            elseif ( $j == $count ) $diff[$key] = $val;
        }
        elseif ( $j == $count && $count ) $diff[$key] = $val;
    }

    return $diff;
}

?>

The following will recursively do an array_diff_assoc, which will calculate differences on a multi-dimensional level.  This not display any notices if a key don't exist and if error_reporting is set to E_ALL:

<?php
function array_diff_assoc_recursive($array1, $array2)
{
    foreach($array1 as $key => $value)
    {
        if(is_array($value))
        {
              if(!isset($array2[$key]))
              {
                  $difference[$key] = $value;
              }
              elseif(!is_array($array2[$key]))
              {
                  $difference[$key] = $value;
              }
              else
              {
                  $new_diff = array_diff_assoc_recursive($value, $array2[$key]);
                  if($new_diff != FALSE)
                  {
                        $difference[$key] = $new_diff;
                  }
              }
          }
          elseif(!isset($array2[$key]) || $array2[$key] != $value)
          {
              $difference[$key] = $value;
          }
    }
    return !isset($difference) ? 0 : $difference;
}
?>

[NOTE BY danbrown AT php DOT net: This is a combination of efforts from previous notes deleted.  Contributors included (Michael Johnson), (jochem AT iamjochem DAWT com), (sc1n AT yahoo DOT com), and (anders DOT carlsson AT mds DOT mdh DOT se).]

Hi all,
For php versions < 4.3...

<?php 
/**
 * array_diff_assoc for version < 4.3
 **/
if (!function_exists('array_diff_assoc'))
{
    function array_diff_assoc($a1, $a2)
    {
        foreach($a1 as $key => $value)
        {
            if(isset($a2[$key]))
            {
                if((string) $value !== (string) $a2[$key])
                {
                     $r[$key] = $value;
                }
            }else
            {
                $r[$key] = $value;
            }
        }
        return $r ;
    }
}

?>

array_diff_assoc will fail, if a value is something that can not be converted to a string.

NOTE: the diff_array also removes all the duplicate values that match to the values in the second array:

<?php
    $array1 = array("a","b","c","a","a");
    $array2 = array("a");

    $diff = array_diff($array1,$array2);

    // yields: array("b","c") the duplicate "a" values are removed 
?>

To unset elements in an array if you know the keys but not the values, you can do:

<?php
$a = array("foo", "bar", "baz", "quux");
$b = array(1, 3); // Elements to get rid of

foreach($b as $e)
  unset($a[$e]);
?>

Of course this makes most sense if $b has many elements or is dynamically generated.

A quite simple (yet not very efficient) way to compare the first level of arrays which have values that are not strings:
array_map('unserialize',array_diff_assoc(array_map('serialize',$arr1),array_map('serialize',$arr2)))
Might be useful for debugging (that's what I use it for).

array_diff_assoc can also be used to find the duplicates in an array

<?php
$arr = array('1','2','3','4','3','2','5');
$uniques = array_unique($arr);
// array_diff will not work here, array_diff_assoc works as it takes the key // in account.
$dups = array_diff_assoc($arr, $uniques);

print_r($dups);
?>

Note: The index of the $dups is not in strict sequential order as expected by C programmer.

To diff between n-dimensional array, juste use this : 

<?php
function array_diff_values($tab1, $tab2)
    {
    $result = array();
    foreach($tab1 as $values) if(! in_array($values, $tab2)) $result[] = $values;
    return $result;
    }
?>

Recursive implementation accepting multiple n-level-arrays as parameters:

<?php
function recursiveDiff() {
    $arrs = func_get_args();
    $first = array_shift($arrs);
    $diff = [];

    foreach($first as $key => $value) {
        $values = array_map(function($arr) use($key){
            if (is_array($arr) && !array_key_exists($key, $arr))
                return null;

            return $arr[$key];
        }, $arrs);

        if (in_array($value, $values))
            continue;

        if (is_array($value)) {
            array_unshift($values, $value);
            $diff[$key] = call_user_func_array(__FUNCTION__, $values);
            continue;
        }

        $diff[$key] = $first[$key];
    }

    return $diff;
}
?>

The other attempt was cleaner but didn't work for all cases.

For recursive diff of multiple arrays, exending solution provided by Gosh.

<?php 

function array_diff_assoc_recursive(array $array, array ...$arrays)
    {
        $func  = function($array1, $array2) use (&$func){
            $difference = [];
            foreach ($array1 as $key => $value) {
                if (is_array($value)) {
                    if (!isset($array2[$key]) || !is_array($array2[$key])) {
                        $difference[$key] = $value;
                    } else {
                        $new_diff = $func($value, $array2[$key]);
                        if (!empty($new_diff)) {
                            $difference[$key] = $new_diff;
                        }
                    }
                } else {
                    if (!array_key_exists($key, $array2) || $array2[$key] !== $value) {
                        $difference[$key] = $value;
                    }
                }
            }
            return $difference;
        };
        $diffs = $array;
        foreach ($arrays as $_array) {
            $diffs = $func($diffs, $_array);
        }
        return $diffs;
    }

?>

function array_diff_assoc_recursive($array1, $array2)
    {
        $array1Array = [];

        foreach ($array1 as $key => $value) {
            if (!is_array($value)) {
                continue;
            }
            $array1Array[$key] = $value;
            unset($array1[$key]);
        }

        $array2Array = [];

        foreach ($array2 as $key => $value) {
            if (!is_array($value)) {
                continue;
            }
            $array2Array[$key] = $value;
            unset($array2[$key]);
        }

        $diff = is_int(array_key_first($array1)) ? array_values(array_diff($array1, $array2)) : array_diff_assoc($array1, $array2);

        foreach ($array1Array as $key => $value) {
            if (isset($array2Array[$key])) {
                $subDiff = array_diff_assoc_recursive($value, $array2Array[$key]);
                if (count($subDiff) !== 0) {
                    $diff = array_merge($diff, is_int($key) ? [$subDiff] : [$key => $subDiff]);
                }
            } else {
                $diff = array_merge($diff, is_int($key) ? [$value] : [$key => $value]);
            }
        }

        return $diff;
    }

Recursive implementation accepting multiple n-level-arrays as parameters:

```php
function recursiveDiff(...$arrays)
{
    $first = array_shift($arrays);
    $diff = [];

    foreach ($first as $key => $value) {
        $values = array_map(function ($arr) use ($key) {
            if (is_array($arr) && !array_key_exists($key, $arr)) {
                return null;
            }

            return isset($arr[$key]) ? $arr[$key] : null;
        }, $arrs);

        if (in_array($value, $values)) {
            continue;
        }

        if (is_array($value)) {
            array_unshift($values, $value);
            $diff[$key] = call_user_func_array(__FUNCTION__, $values);
            continue;
        }

        $diff[$key] = $first[$key];
    }

    return $diff;
}
```

PHP associative keys are case-sensitive, key "a" is different from key "A":

<?php
$arr = ["A" => 666];
var_dump($arr["a"]);
var_dump($arr["A"]);
?>

produces:
NULL
int(666)

And in the same way, array_diff_assoc treats keys case-sensitively, and key "A" is not equal to key "a" and will be diffed:

<?php
// in arrays below value of "a" and "A" are the same, but keys are different
// values of "b" are different
// values of "c" are the same
$compareWhat = ["a" => 666, "b" => 666, "c" => 666, ];
$compareWith = ["A" => 666, "b" => 667, "c" => 666, ];

var_dump(array_diff_assoc($compareWhat, $compareWith));
?>

produces:
array(2) {
["a"]=> int(666)
["b"]=> int(666)
}

And if the order of values in array is different, the order of the result will be different, although essentially the result stays the same:

<?php
// the same as above, but "b" comes before "a" in $compareWhat 
$compareWhat = ["b" => 666, "a" => 666, "c" => 666, ];
$compareWith = ["A" => 666, "b" => 667, "c" => 666, ];

var_dump(array_diff_assoc($compareWhat, $compareWith));
?>

produces:
array(2) {
["b"]=> int(666)
["a"]=> int(666)
}

there is a functiont that i searched long enough now i have created it so someone else to find it if he need it ;]
<?php
    function compare_two_object_recursive($object_1, $object_2, $object_1_Identifier = false, $object_2_Identifier = false){
        $object1 = (array)$object_1;
        $object2 = (array)$object_2;
        $object3 = array();

        $o1i = $object_1_Identifier ? $object_1_Identifier : 1;
        $o2i = $object_2_Identifier ? $object_2_Identifier : 2;

        foreach($object1 as $key => $value){
            if(is_object($object1[$key])){
                $object1[$key] = (array)$object1[$key];
                $object2[$key] = (array)$object2[$key];
                $object3[$key] = (object)compare_two_object_recursive($object1[$key], $object2[$key], $o1i, $o2i);
            }elseif(is_array($object1[$key])){
                $object3[$key] = compare_two_object_recursive($object1[$key], $object2[$key], $o1i, $o2i);
            }else{
                if($object1[$key] == $object2[$key]){
                    $object3[$key]['comparison_status'] = "SAME";
                }else{
                    $object3[$key]['comparison_status'] = "NOT THE SAME";
                    $object3[$key][$o1i] = $object1[$key];
                    $object3[$key][$o2i] = $object2[$key];
                }
            }
        }
        return $object3;
    }
?>

to chinello at gmail dot com
I've had to use your function but it showed that the use of isset can't differentiate the NULL values from not setted values.

Here's a version that takes care of this subtility.
 
<?php
function array_diff_assoc_recursive($array1, $array2)
{
    $difference = NULL;
    foreach($array1 as $key => $value)
    {
        if(is_array($value))
        {
            if(!array_key_exists($key, $array2))
            {
                $difference[$key] = $value;
            }
            elseif(!is_array($array2[$key]))
            {
                $difference[$key] = $value;
            }
            else
            {
                $new_diff = array_diff_assoc_recursive($value, $array2[$key]);
                if($new_diff != FALSE)
                {
                    $difference[$key] = $new_diff;
                }
            }
        }
        elseif(!array_key_exists($key, $array2) || $array2[$key] != $value)
        {
            $difference[$key] = $value;
        }
    }
    return !isset($difference) ? 0 : $difference;
}
?>

Hope that helps
François

Yet another recursive implementation, without if-else hell and with multiple parameters just like the original.

<?php
function recursiveDiff() {
    $arrs = func_get_args();
    $diff = call_user_func_array('array_diff_assoc', $arrs);

    foreach($diff as $key => $value) {
        if (!is_array($value))
            continue;

        $children = array_map(function($arr) use($key){
            return $arr[$key];
        }, $arrs);

        $diff[$key] = call_user_func_array(__FUNCTION__, $children);
    }

    return $diff;
}