0
在线手册:中文 英文

array_diff

(PHP 4 >= 4.0.1, PHP 5, PHP 7, PHP 8)

array_diff计算数组的差集

说明

array_diff(array $array, array ...$arrays): array

对比 array 和其他一个或者多个数组,返回在 array 中但是不在其他 array 里的值。

参数

array

要被对比的数组

arrays

和更多数组进行比较

返回值

返回一个数组,该数组包括了所有在 array 中但是不在任何其它参数数组中的值。注意键名保留不变。 保留数组 array 里的键。

范例

示例 #1 array_diff() 例子

<?php
$array1 
= array("a" => "green""red""blue""red");
$array2 = array("b" => "green""yellow""red");
$result array_diff($array1$array2);

print_r($result);
?>

$array1 中多次出现的值一样处理,输出结果为:

Array
(
    [1] => blue
)

示例 #2 array_diff() example with non-matching types

两个元素只有在 (string) $elem1 === (string) $elem2 相等时视为一致。 也就是字符串转换表达相同。

<?php
// 数组无法转换成字符串时会产生 Notice 警告
$source = [1234];
$filter = [34, [5], 6];
$result array_diff($source$filter);

// 而这个就可以,因为对象可以转换成字符串
class {
  private 
$v;

  public function 
__construct(string $v) {
    
$this->$v;
  }

  public function 
__toString() {
    return 
$this->v;
  }
}

$source = [new S('a'), new S('b'), new S('c')];
$filter = [new S('b'), new S('c'), new S('d')];

$result array_diff($source$filter);

// $result 包含了一个 S('a'); 实例
?>

想要使用函数来比较,可使用 array_udiff()

注释

注意:

注意本函数只检查了多维数组中的一维。当然可以用 array_diff($array1[0], $array2[0]); 检查更深的维度。

参见

0
在线手册:中文 英文

27位用户评论

[#1] ▲3▼ al amin chayan (mail@chayan.me) [100%] (2020-09-21 16:17:12)

<?php
/**
   * Check If An Array Is A Subset Of Another Array
   *
   * @param  array $subset
   * @param  array $set
   * @return bool
   */
function is_subset(array $subset, array $set): bool {
     return (bool)!
array_diff($subset$set);
}

$u = [156810];
$a = [15];
$b = [67];

var_dump(is_subset($a$u)); // true
var_dump(is_subset($b$u)); // false

[#2] ▲2▼ prakashgun [100%] (2017-12-11 12:04:31)

If duplicate value comes in the first array, that will be also included. See in the output "blue" comes twice. <?php

$array1 
= array("a" => "green""red""blue""red""blue");
$array2 = array("b" => "green""yellow""red");
$result array_diff($array1$array2);

print_r($result);

//Output
//Array ( [1] => blue [3] => blue )

[#3] ▲3▼ wes.melton@gmail.com [80%] (2017-06-20 21:11:26)

It's important to note that array_diff() is NOT a fast or memory-efficient function on larger arrays. In my experience, when I find myself running array_diff() on larger arrays (50+ k/v/pairs) I almost always realize that I'm working the problem from the wrong angle. Typically, when reworking the problem to not require array_diff(), especially on bigger datasets, I find significant performance improvements and optimizations.

[#4] ▲28▼ james.plznospam@bush.cc [76%] (2017-03-16 13:58:20)

If you want a simple way to show values that are in either array, but not both, you can use this: <?php
function arrayDiff($A$B) {
    
$intersect array_intersect($A$B);
    return 
array_merge(array_diff($A$intersect), array_diff($B$intersect));
}
?>
If you want to account for keys, use array_diff_assoc() instead; and if you want to remove empty values, use array_filter().

[#5] ▲0▼ emeka.echeruo@gmail.com [50%] (2016-05-10 15:49:49)

Resubmitting... the update for takes into account comparison issues Computes the difference of all the arrays <?php 

/**
 * array_diffs â€” Computes the difference of all the arrays 
 * 
 * @param array 
 * 
 *    array1 - The array to compare from and against
 *    array2 - The array to compare from and against
 *    array(n) - More arrays to compare from and against
 *        
 * @return array Returns all the arrays that do contains entries that cannot be matched in any of the arrays.
 */
 
function array_diffs() {
    
$count func_num_args();
    if(
$count 2) {
        
trigger_error('Must provide at least 2 arrays for comparison.');
    }
    
$check = array();
    
$out = array();
     
//resolve comparison issue
    
$func = function($a$b) {
        
$dbl = function($i$d) {
            
$e 0.00001;
            if(
abs($i-$d) < $e) {
                return 
true;
            }
            return 
false;
        };
        if((
gettype($a) == 'integer' && gettype($b['value']) == 'double') || (gettype($a) == 'double' && gettype($b['value']) == 'integer')) {
            if((
gettype($a) == 'integer' && $dbl((double) $a$b['value'])) || (gettype($b['value']) == 'integer' && $dbl((double) $b['value'], $a))) {
                return 
true;
            }
        } elseif((
gettype($a) == 'double') && (gettype($b['value']) == 'double')) {
            return 
$dbl($a,$b['value']);
        } elseif(
$a == $b['value']) {
            return 
true;
        }
        return 
false;
    };
    for(
$i 0$i $count$i++) {
        if(!
is_array(func_get_arg($i))) {
            
trigger_error('Parameters must be passed as arrays.');
        }
        foreach(
func_get_arg($i) as $key => $value) {
            if(
is_numeric($key) && is_string($value)) {
                if(
array_key_exists($value$check) && $func($value$check[$value])) {
                    
$check[$value]['count'] = $check[$value]['count'] + 1;
                } else {
                    
$check[$value]['value'] = $value;
                    
$check[$value]['count'] = 1;
                }
            } elseif(
is_numeric($key) && (is_bool($value) || is_null($value) || is_numeric($value) || is_object($value) || is_resource($value))) {
                
$update false;
                foreach(
$check as $check_key => $check_value) {
                    if(
is_numeric($key) && (is_bool($check_value['value']) || is_null($check_value['value']) || is_numeric($check_value['value']) || is_object($check_value['value']) || is_resource($check_value['value'])) && $func($value$check_value)) {
                        
$update true;
                        
$check[$check_key]['count'] = $check[$check_key]['count'] + 1;
                    } 
                }
                if(!
$update) {
                    
$check[] = array('value' => $value'count' => 1);
                }
            } else {
                if(
array_key_exists($key$check) && $func($value$check[$key])) {
                    
$check[$key]['count'] = $check[$key]['count'] + 1;
                } else {
                    
$check[$key]['value'] = $value;
                    
$check[$key]['count'] = 1;
                }
            }
        }
    }
    foreach(
$check as $check_key => $check_value) {
        if(
$check_value['count'] == 1) {
           for (
$i 0$i $count$i++) {
                foreach(
func_get_arg($i) as $key => $value) {
                    if(
is_numeric($key) && is_string($value) && ($value == (string) $check_key)) {
                        
$out[$i][$key] = $value;
                    } elseif(
is_numeric($key) && ($check_value['value'] == $value)) {
                        
$out[$i][$key] = $value;
                    } elseif(
is_string($key) && ($check_value['value'] == $value)) {
                        
$out[$i][$key] = $value;
                    }
                }
            }
        }
    }
    return 
$out;
}

?>

[#6] ▲3▼ emeka@echeruo@gmail.com [60%] (2016-04-30 11:10:36)

Resubmitting... the update for takes into account comparison issues Computes the difference of all the arrays <?php

/**
 * array_diffs — Computes the difference of all the arrays 
 * 
 * @param array 
 * 
 *    array1 - The array to compare from and against
 *    array2 - The array to compare from and against
 *    array(n) - More arrays to compare from and against
 *        
 * @return array Returns all the arrays that do contains entries that cannot be matched in any of the arrays.  
 */
 
function array_diffs() {
    
$count func_num_args();
    if(
$count 2) {
        
trigger_error('Must provide at least 2 arrays for comparison.');
    }
    
$check = array();
    
$out = array();
     
//resolve comparison issues in PHP
    
$func = function($a$b) {
        if(
gettype($a) == 'integer' && gettype($b['value']) == 'double' || gettype($a) == 'double' && gettype($b['value']) == 'integer') {
            if(
gettype($a) == 'integer') {
                if((double) 
$a == $b['value']) {
                    return 
true;
                }
            } else {
                if((double) 
$b['value'] == $a) {
                    return 
true;
                }
            }
        } elseif(
gettype($a) == 'double' && gettype($b['value']) == 'double') {
            
$epsilon 0.00001;
            if(
abs($a $b['value']) < $epsilon) {
                return 
true;
            }
        } else {
            if(
$a == $b['value']) {
                return 
true;
            }
        }
        return 
false;
    };
    for (
$i 0$i $count$i++) {
        if(!
is_array(func_get_arg($i))) {
            
trigger_error('Parameters must be passed as arrays.');
        }
        foreach(
func_get_arg($i) as $key => $value) {
            if(
is_numeric($key) && is_string($value)) {
                if(
array_key_exists($value$check) && $func($value$check[$value])) {
                    
$check[$value]['count'] = $check[$value]['count'] + 1;
                } else {
                    
$check[$value]['value'] = $value;
                    
$check[$value]['count'] = 1;
                }
            } elseif(
is_numeric($key) && (is_bool($value) || is_null($value) || is_numeric($value) || is_object($value) || is_resource($value))) {
                
$update false;
                foreach(
$check as $check_key => $check_value) {
                    if(
is_numeric($key) && (is_bool($check_value['value']) || is_null($check_value['value']) || is_numeric($check_value['value']) || is_object($check_value['value']) || is_resource($check_value['value']))) {
                        if(
$func($value$check_value)) {
                            
$update true;
                            
$check[$check_key]['count'] = $check[$check_key]['count'] + 1;
                        }
                    } 
                }
                if(!
$update) {
                    
$check[] = array('value' => $value'count' => 1);
                }
            } else {
                if(
array_key_exists($key$check) && $func($value$check[$key])) {
                    
$check[$key]['count'] = $check[$key]['count'] + 1;
                } else {
                    
$check[$key]['value'] = $value;
                    
$check[$key]['count'] = 1;
                }
            }
        }
    }
    foreach(
$check as $check_key => $check_value) {
        if(
$check_value['count'] == 1) {
            for (
$i 0$i $count$i++) {
                foreach(
func_get_arg($i) as $key => $value) {
                    if(
is_numeric($key) && is_string($value)) {
                        if(
$value == (string) $check_key) {
                            
$out[$i][$key] = $value;
                        }
                    } elseif(
is_numeric($key) && (is_bool($value) || is_null($value) || is_numeric($value) || is_object($value) || is_resource($value))) { 
                        if(
is_numeric($key) && (is_bool($check_value['value']) || is_null($check_value['value']) || is_numeric($check_value['value']) || is_object($check_value['value']) || is_resource($check_value['value']))) {
                            if(
$check_value['value'] == $value) {
                                
$out[$i][$key] = $value;
                            }
                        }
                    } else {
                        if(
$key == $check_key) {
                            
$out[$i][$key] = $value;
                        }
                    }
                }
            }
        }
    }
    return 
$out;
}

?>

[#7] ▲6▼ anonymous [62%] (2015-05-05 06:50:19)

I always wanted something like this to avoid listing all the files and folders you want to exclude in a project directory. function array_preg_diff($a, $p) { foreach ($a as $i => $v) if (preg_match($p, $v)) unset($a[$i]); return $a; } $relevantFiles = array_preg_diff(scandir('somedir'), '/^\./'); instead of $relevantFiles = array_diff(scandir('somedir'), array('.', '..', '.idea', '.project));

[#8] ▲1▼ anonymous [67%] (2015-01-28 16:00:00)

If you're not getting a count(array_diff($a1,$a2))>0 with something similar to the following arrays should use the php.net/array_diff_assoc function instead. $a1 = Array ( [0] => id [1] => id_1 [2] => id_2 ) $a2 = Array ( [0] => id [1] => id_2 [2] => id_1 )

[#9] ▲2▼ wrey75@gmail.com [57%] (2014-12-03 22:27:00)

The difference is made only on the first level. If you want compare 2 arrays, you can use the code available at https://gist.github.com/wrey75/c631f6fe9c975354aec7 (including a class with an function to patch the array) Here the basic function: function my_array_diff($arr1, $arr2) { $diff = array(); // Check the similarities foreach( $arr1 as $k1=>$v1 ){ if( isset( $arr2[$k1]) ){ $v2 = $arr2[$k1]; if( is_array($v1) && is_array($v2) ){ // 2 arrays: just go further... // .. and explain it's an update! $changes = self::diff($v1, $v2); if( count($changes) > 0 ){ // If we have no change, simply ignore $diff[$k1] = array('upd' => $changes); } unset($arr2[$k1]); // don't forget } else if( $v2 === $v1 ){ // unset the value on the second array // for the "surplus" unset( $arr2[$k1] ); } else { // Don't mind if arrays or not. $diff[$k1] = array( 'old' => $v1, 'new'=>$v2 ); unset( $arr2[$k1] ); } } else { // remove information $diff[$k1] = array( 'old' => $v1 ); } } // Now, check for new stuff in $arr2 reset( $arr2 ); // Don't argue it's unnecessary (even I believe you) foreach( $arr2 as $k=>$v ){ // OK, it is quite stupid my friend $diff[$k] = array( 'new' => $v ); } return $diff; }

[#10] ▲35▼ jeppe utzon [66%] (2012-11-08 14:28:09)

If you just need to know if two arrays' values are exactly the same (regardless of keys and order), then instead of using array_diff, this is a simple method: <?php

function identical_values$arrayA $arrayB ) {

    
sort$arrayA );
    
sort$arrayB );

    return 
$arrayA == $arrayB;
}

// Examples:

$array1 = array( "red" "green" "blue" );
$array2 = array( "green" "red" "blue" );
$array3 = array( "red" "green" "blue" "yellow" );
$array4 = array( "red" "yellow" "blue" );
$array5 = array( "x" => "red" "y" =>  "green" "z" => "blue" );

identical_values$array1 $array2 );  // true
identical_values$array1 $array3 );  // false
identical_values$array1 $array4 );  // false
identical_values$array1 $array5 );  // true

?>
The function returns true only if the two arrays contain the same number of values and each value in one array has an exact duplicate in the other array. Everything else will return false. my alternative method for evaluating if two arrays contain (all) identical values: <?php

sort
($a); $sort(b); return $a == $b;

?>
may be slightly faster (10-20%) than this array_diff method: <?php

return ( count$a ) == count$b ) && !array_diff$a $b ) ? true false );

?>
but only when the two arrays contain the same number of values and then only in some cases. Otherwise the latter method will be radically faster due to the use of a count() test before the array_diff(). Also, if the two arrays contain a different number of values, then which method is faster will depend on whether both arrays need to be sorted or not. Two times sort() is a bit slower than one time array_diff(), but if one of the arrays have already been sorted, then you only have to sort the other array and this will be almost twice as fast as array_diff(). Basically: 2 x sort() is slower than 1 x array_diff() is slower than 1 x sort().

[#11] ▲12▼ merlyn.tgz@gmail.com [64%] (2012-03-15 10:08:10)

There is more fast implementation of array_diff, but with some limitations. If you need compare two arrays of integers or strings you can use such function: public static function arrayDiffEmulation($arrayFrom, $arrayAgainst) { $arrayAgainst = array_flip($arrayAgainst); foreach ($arrayFrom as $key => $value) { if(isset($arrayAgainst[$value])) { unset($arrayFrom[$key]); } } return $arrayFrom; } It is ~10x faster than array_diff php > $t = microtime(true);$a = range(0,25000); $b = range(15000,500000); $c = array_diff($a, $b);echo microtime(true) - $t; 4.4335179328918 php > $t = microtime(true);$a = range(0,25000); $b = range(15000,500000); $c = arrayDiffEmulation($a, $b);echo microtime(true) - $t; 0.37219095230103

[#12] ▲2▼ eugeny.yakimovitch@gmail.com [58%] (2010-12-30 03:17:13)

Note that array_diff is not equivalent to <?php
function fullArrayDiff($left$right
{
    return 
array_diff(array_merge($left$right), array_intersect($left$right));
}
?>
since it is a set-theoretical complement as in http://en.wikipedia.org/wiki/Complement_(set_theory)

[#13] ▲2▼ javierchinapequeno@yahoo.es [57%] (2010-12-21 11:21:09)

Hi, I´d like to give a piece of advice to all who need to use this function to compare two arrays that have a great quantity of elements. You should sort both arrays first before comparing, it will work faster. Thanks

[#14] ▲3▼ vojtech.hordejcuk@gmail.com [57%] (2009-11-03 07:15:51)

Based on one lad's code, I created following function for creating something like HTML diff. I hope it will be useful. <?php
private function diff ($old$new)
{
  
$old preg_replace ('/ +/'' '$old);
  
$new preg_replace ('/ +/'' '$new);
  
  
$lo explode ("\n"trim ($old) . "\n");
  
$ln explode ("\n"trim ($new) . "\n");
  
$size max (count ($lo), count ($ln));

  
$equ array_intersect ($lo$ln);
  
$ins array_diff ($ln$lo);
  
$del array_diff ($lo$ln);
  
  
$out '';
  
  for (
$i 0$i $size$i++)
  {
    if (isset (
$del [$i]))
    {
      
$out .= '<p><del>' $del [$i] . '</del></p>';
    }
    
    if (isset (
$equ [$i]))
    {
      
$out .= '<p>' $equ [$i] . '</p>';
    }
    
    if (isset (
$ins [$i]))
    {
      
$out .= '<p><ins>' $ins [$i] . '</ins></p>';
    }
  }
  
  return 
$out;
}
?>

[#15] ▲2▼ anonymous [56%] (2009-10-15 11:55:30)

Hi! I tried hard to find a solution to a problem I'm going to explain here, and after have read all the array functions and possibilities, I had to create what I think should exist on next PHP releases. What I needed, it's some kind of Difference, but working with two arrays and modifying them at time, not returning an array as a result with the diference itself. So, as an example: A = 1,2,3 B = 2,3,4 should NOT be: C = 1,4 but: A = 1 B = 4 so basically, I wanted to delete coincidences on both arrays. Now, I've some actions to do, and I know wich one I've to do with the values from one array or another. With the normal DIFF I can't, because if I've an array like C=1,4, I dont know if I've to do the Action_A with 1 or with 4, but I really know that everything in A, will go to the Action_A and everithing in B, will go to Action_B. So same happens with 4, don't know wich action to apply... So I created this: <?php
function array_diff_ORG_NEW(&$org, &$new$type='VALUES'){
    switch(
$type){
        case 
'VALUES':
            
$int array_values(array_intersect($org$new)); //C = A ^ B
            
$org array_values(array_diff($org$int)); //A' = A - C
            
$newarray_values(array_diff($new$int)); //B' = B - C
            
break;
        case 
'KEYS':
            
$int array_values(array_intersect_key($org$new)); //C = A ^ B
            
$org array_values(array_diff_key($org$int)); //A' = A - C
            
$newarray_values(array_diff_key($new$int)); //B' = B - C
            
break;
    }
}
?>
This cute, works by reference, and modifies the arrays deleting coincidences on both, and leaving intact the non coincidences. So a call to this will be somethin' like: <?php
$original 
= array(1,2,3);
$new = array(2,3,4);

array_diff_ORG_NEW($original$new'VALUES');
?>
And HERE, I'll have my arrays as I wanted: $original = 1 $new = 4 Now, why I use it precisely? Imagine you've some "Events" and some users you select when create the event, can "see" this event you create. So you "share" the event with some users. Ok? Imagine you created and Event_A, and shared with users 1,2,3. Now you want to modify the event, and you decide to modify the users to share it. Imagine you change it to users 2,3,4. (numbers are users ID). So you can manage when you are going to modify, to have an array with the IDs in DDBB ($original), and then, have another array with ID's corresponding to the users to share after modifying ($new). Wich ones you've to DELETE from DDBB, and wich ones do you've to INSERT? If you do a simple difference or somehow, you get somethin' like C=1,4. You have no clue on wich one you've to insert or delete. But on this way, you can know it, and that's why: - What keeps on $original, it's somethin not existing in $new at the beggining. So you know that all what you've inside $original, have to be deleted from DDBB because what you did in the modifying process, it's to unselect those users keeping in $original. - What keeps on $new, it's something not existing in $original at the beggining. Wich means that in the modifying process you added some new users. And those have to be inserted in DDBB. So, everything keeping inside $new, have to be inserted in the DDBB. Conclusion: - Remaining in $original --> delete from DB. - Remaining in $new --> insert into DB. And that's all! I hope you find it useful, and I encourage PHP "makers", to add in a not distant future, somethin' like this one natively, because I'm shure that I'm not the first one needing something like this. Best regards all, Light.

[#16] ▲21▼ firegun@terra.com.br [72%] (2009-06-24 10:52:59)

Hello guys, I´ve been looking for a array_diff that works with recursive arrays, I´ve tried the ottodenn at gmail dot com function but to my case it doesn´t worked as expected, so I made my own. I´ve haven´t tested this extensively, but I´ll explain my scenario, and this works great at that case :D We got 2 arrays like these: <?php
$aArray1
['marcie'] = array('banana' => 1'orange' => 1'pasta' => 1);
$aArray1['kenji'] = array('apple' => 1'pie' => 1'pasta' => 1);

$aArray2['marcie'] = array('banana' => 1'orange' => 1);
?>
As array_diff, this function returns all the items that is in aArray1 and IS NOT at aArray2, so the result we should expect is: <?php
$aDiff
['marcie'] = array('pasta' => 1);
$aDiff['kenji'] = array('apple' => 1'pie' => 1'pasta' => 1);
?>
Ok, now some comments about this function: - Different from the PHP array_diff, this function DON´T uses the === operator, but the ==, so 0 is equal to '0' or false, but this can be changed with no impacts. - This function checks the keys of the arrays, array_diff only compares the values. I realy hopes that this could help some1 as I´ve been helped a lot with some users experiences. (Just please double check if it would work for your case, as I sad I just tested to a scenario like the one I exposed) <?php
function arrayRecursiveDiff($aArray1$aArray2) {
    
$aReturn = array();
   
    foreach (
$aArray1 as $mKey => $mValue) {
        if (
array_key_exists($mKey$aArray2)) {
            if (
is_array($mValue)) {
                
$aRecursiveDiff arrayRecursiveDiff($mValue$aArray2[$mKey]);
                if (
count($aRecursiveDiff)) { $aReturn[$mKey] = $aRecursiveDiff; }
            } else {
                if (
$mValue != $aArray2[$mKey]) {
                    
$aReturn[$mKey] = $mValue;
                }
            }
        } else {
            
$aReturn[$mKey] = $mValue;
        }
    }
   
    return 
$aReturn;
}
?>

[#17] ▲3▼ tim trefren [67%] (2008-04-04 08:05:53)

Here's a little wrapper for array_diff - I found myself needing to iterate through the edited array, and I didn't need to original keys for anything. <?php
function arrayDiff($array1$array2){
    
# This wrapper for array_diff rekeys the array returned
    
$valid_array array_diff($array1,$array2);
    
    
# reinstantiate $array1 variable 
    
$array1 = array();
    
    
# loop through the validated array and move elements to $array1
    # this is necessary because the array_diff function returns arrays that retain their original keys
    
foreach ($valid_array as $valid){
        
$array1[] = $valid;
        }
    return 
$array1;
    }
?>

[#18] ▲3▼ merlinyoda@dorproject.net [62%] (2008-03-28 10:11:00)

As touched on in kitchin's comment of 19-Jun-2007 03:49 and nilsandre at gmx dot de's comment of 17-Jul-2007 10:45, array_diff's behavior may be counter-intuitive if you aren't thinking in terms of set theory. array_diff() returns a *mathematical* difference (a.k.a. subtraction) of elements in array A that are in array B and *not* what elements are different between the arrays (i.e. those that elements that are in either A or B but aren't in both A and B). Drawing one of those Ven diagrams or Euler diagrams may help with visualization... As far as a function for returning what you may be expecting, here's one: <?php 
function array_xor ($array_a$array_b) {
    
$union_array array_merge($array_a$array_b);
    
$intersect_array array_intersect($array_a$array_b);
    return 
array_diff($union_array$intersect_array)
}
?>

[#19] ▲201▼ nilsandre@gmx.de [76%] (2007-07-17 09:45:24)

Again, the function's description is misleading right now. I sought a function, which (mathematically) computes A - B, or, written differently, A \ B. Or, again in other words, suppose A := {a1, ..., an} and B:= {a1, b1, ... , bm} => array_diff(A,B) = {a2, ..., an} array_diff(A,B) returns all elements from A, which are not elements of B (= A without B). You should include this in the documentation more precisely, I think.

[#20] ▲1▼ gilthans@nogmailspam.com [54%] (2007-06-13 10:11:30)

I needed a function to only remove the element the amount of times he appears in the second array. In other words, if you have Array(1, 1, 2) and Array(1), the return value should be Array(1, 2). So I built this function right here: <?php
function array_diff_once(){
    if((
$args func_num_args()) < 2)
        return 
false;
    
$arr1 func_get_arg(0);
    
$arr2 func_get_arg(1);
    if(!
is_array($arr1) || !is_array($arr2))
        return 
false;
    foreach(
$arr2 as $remove){
        foreach(
$arr1 as $k=>$v){
            if((string)
$v === (string)$remove){ //NOTE: if you need the diff to be STRICT, remove both the '(string)'s
                
unset($arr1[$k]);
                break; 
//That's pretty much the only difference from the real array_diff :P
            
}
        }
    }
    
//Handle more than 2 arguments
    
$c $args;
    while(
$c 2){
        
$c--;
        
$arr1 array_diff_once($arr1func_get_arg($args-$c+1));
    }
    return 
$arr1;
}
$arr1 = Array("blue""four"=>4"color"=>"red""blue""green""green""name"=>"jon""green");
$arr2 = Array("4""red""blue""green");
print_r(array_diff_once($arr1$arr2));
?>
This prints: Array ( [1] => blue [3] => green [name] => jon [4] => green ) Note that it removes the elements left to right, opposite to what you might expect; in my case the order of elements had no importance. Fixing that would require a small variation.

[#21] ▲55▼ (2006-08-03 12:30:30)

array_diff provides a handy way of deleting array elements by their value, without having to unset it by key, through a lengthy foreach loop and then having to rekey the array. <?php

//pass value you wish to delete and the array to delete from
function array_delete$value$array)
{
    
$array array_diff$array, array($value) );
    return 
$array;
}
?>

[#22] ▲3▼ simon riget@paragi.dk [58%] (2006-01-21 17:27:34)

A simple multidimentional key aware array_diff function. <?php    
function arr_diff($a1,$a2){
  foreach(
$a1 as $k=>$v){
    unset(
$dv);
    if(
is_int($k)){
      
// Compare values
      
if(array_search($v,$a2)===false$dv=$v;
      else if(
is_array($v)) $dv=arr_diff($v,$a2[$k]);
      if(
$dv$diff[]=$dv;
    }else{
      
// Compare noninteger keys
      
if(!$a2[$k]) $dv=$v;
      else if(
is_array($v)) $dv=arr_diff($v,$a2[$k]);
      if(
$dv$diff[$k]=$dv;
    }    
  }
  return 
$diff;
}
?>
This function meets my immidiate needs but I'm shure it can be improved.

[#23] ▲1▼ viking coder [53%] (2006-01-03 09:07:12)

To anybody wanting a double-sided array_diff - mentioned by rudigier at noxx dot at. Remember, array_diff gives you everything in the first array that isn't in the subsequent arrays. $array1=array('blue','red','green'); $array2=array('blue','yellow','green'); array_merge(array_diff($array1, $array2),array_diff($array2, $array1)); Result ------ Array ( [0] => red [1] => yellow )

[#24] ▲1▼ j.j.d.mol@ewi.tudelft.nl [57%] (2004-12-31 00:34:12)

Here is some code to take the difference of two arrays. It allows custom modifications like prefixing with a certain string (as shown) or custom compare functions. <?php 
 
// returns all elements in $all which are not in $used in O(n log n) time.
  // elements from $all are prefixed with $prefix_all.
  // elements from $used are prefixed with $prefix_used.
  
function filter_unused$all$used$prefix_all ""$prefix_used "" ) {
      
$unused = array();

      
// prefixes are not needed for sorting
      
sort$all );
      
sort$used );

      
$a 0;
      
$u 0;

      
$maxa sizeof($all)-1;
      
$maxu sizeof($used)-1;

      while( 
true ) {
          if( 
$a $maxa ) {
              
// done; rest of $used isn't in $all
              
break;
          }
          if( 
$u $maxu ) {
              
// rest of $all is unused
              
for( ; $a <= $maxa$a++ ) {
                  
$unused[] = $all[$a];
              }
              break;
          }

          if( 
$prefix_all.$all[$a] > $prefix_used.$used[$u] ) {
              
// $used[$u] isn't in $all?
              
$u++;
              continue;
          }

          if( 
$prefix_all.$all[$a] == $prefix_used.$used[$u] ) {
              
// $all[$a] is used
              
$a++;
              
$u++;
              continue;
          }

          
$unused[] = $all[$a];

          
$a++;
      }

      return 
$unused;
  }
?>

[#25] ▲4▼ (2003-11-18 16:54:26)

From the page: Note: Please note that this function only checks one dimension of a n-dimensional array. Of course you can check deeper dimensions by using array_diff($array1['0'], $array2['0']); I've found a way to bypass that. I had 2 arrays made of arrays. I wanted to extract from the first array all the arrays not found in the second array. So I used the serialize() function: <?php
function my_serialize(&$arr,$pos){
  
$arr serialize($arr);
}

function 
my_unserialize(&$arr,$pos){
  
$arr unserialize($arr);
}

 
//make a copy
$first_array_s $first_array;
$second_array_s $second_array;

// serialize all sub-arrays
array_walk($first_array_s,'my_serialize'); 
array_walk($second_array_s,'my_serialize');

// array_diff the serialized versions
$diff array_diff($first_array_s,$second_array_s);

// unserialize the result
array_walk($diff,'my_unserialize');

// you've got it!
print_r($diff);
?>

[#26] ▲2▼ ds2u @the hotmail . com [60%] (2003-02-23 16:22:05)

Yes you can get rid of gaps/missing keys by using: <?php
$result 
array_values(array_diff($array1,$array2));
?>
But to drop the storage of void spaces (actually a line feed) which are irritatingly indexed when reading from files - just use difference: <?php
$array 
= array ();
$array[0] = "\n";
$result array_diff($result,$array);
?>
dst

[#27] ▲25▼ seanecoates@!donotspam!yahoo.ca [73%] (2001-10-16 10:43:45)

I just came upon a really good use for array_diff(). When reading a dir(opendir;readdir), I _rarely_ want "." or ".." to be in the array of files I'm creating. Here's a simple way to remove them: <?php
 $someFiles 
= array();
 
$dp opendir("/some/dir");
 while(
$someFiles[] = readdir($dp));
 
closedir($dp);
 
 
$removeDirs = array(".","..");
 
$someFiles array_diff($someFiles$removeDirs);
 
 foreach(
$someFiles AS $thisFile) echo $thisFile."\n";
?>
S