PHP 5.6.0RC3 is available

array_diff

(PHP 4 >= 4.0.1, PHP 5)

array_diffCalcule la différence entre des tableaux

Description

array array_diff ( array $array1 , array $array2 [, array $... ] )

array_diff() compare le tableau array1 avec un ou plusieurs tableaux et retourne les valeurs du tableaux array1 qui ne sont pas présentes dans les autres tableaux.

Liste de paramètres

array1

Le tableau depuis lequel comparer

array2

Un tableau avec lequel comparer

...

Plus de tableaux avec lesquels comparer

Valeurs de retour

Retourne un tableau contenant toutes les entités du tableau array1 qui ne sont présentes dans aucun des autres tableaux.

Exemples

Exemple #1 Exemple avec array_diff()

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

print_r($result);
?>

Les valeurs multiples dans array1 seront toutes traitées de la même façon. Ce qui affichera :

Array
(
    [1] => blue
)

Notes

Note:

Deux éléments sont considérés comme égaux si et seulement si (string) $elem1 === (string) $elem2. En clair : lorsque la représentation sous forme de chaîne de caractères est identique.

Note:

Notez que cette fonction ne vérifie qu'une seule dimension d'un tableau à plusieurs dimensions. Bien sûr, vous pouvez vérifier des dimensions plus profondes en utilisant array_diff($array1[0], $array2[0]);.

Voir aussi

add a note add a note

User Contributed Notes 43 notes

up
29
nilsandre at gmx dot de
7 years ago
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.
up
11
Jeppe Utzon
1 year ago
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().
up
5
SeanECoates at !donotspam!yahoo dot ca
12 years ago
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
up
10
merlyn dot tgz at gmail dot com
2 years ago
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
up
4
javierchinapequeno at yahoo dot es
3 years ago
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
up
6
vojtech dot hordejcuk at gmail dot com
4 years ago
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;
}
?>
up
6
mr dot kschan at gmail dot com
7 years ago
just comment ... i don't know whether the following implementation of array_diff is having a much better meaning to the function name.

function ary_diff( $ary_1, $ary_2 ) {
  // compare the value of 2 array
  // get differences that in ary_1 but not in ary_2
  // get difference that in ary_2 but not in ary_1
  // return the unique difference between value of 2 array
  $diff = array();

  // get differences that in ary_1 but not in ary_2
  foreach ( $ary_1 as $v1 ) {
    $flag = 0;
    foreach ( $ary_2 as $v2 ) {
      $flag |= ( $v1 == $v2 );
      if ( $flag ) break;
    }
    if ( !$flag ) array_push( $diff, $v1 );
  }

  // get difference that in ary_2 but not in ary_1
  foreach ( $ary_2 as $v2 ) {
    $flag = 0;
    foreach ( $ary_1 as $v1 ) {
      $flag |= ( $v1 == $v2 );
      if ( $flag ) break;
    }
    if ( !$flag && !in_array( $v2, $diff ) ) array_push( $diff, $v2 );
  }

  return $diff;
}

i think array_diff should return the difference between the array independent of the order of passing the parameter.
up
3
csaba2000 at yahoo dot com
11 years ago
<?php
function array_key_diff($ar1, $ar2) {  // , $ar3, $ar4, ...
    // returns copy of array $ar1 with those entries removed
    // whose keys appear as keys in any of the other function args
   
$aSubtrahends = array_slice(func_get_args(),1);
    foreach (
$ar1 as $key => $val)
        foreach (
$aSubtrahends as $aSubtrahend)
            if (
array_key_exists($key, $aSubtrahend))
                unset (
$ar1[$key]);
    return
$ar1;
}

$a = array("c" => "catty", "b" => "batty", "a" => "aunty", 5 => 4, 2.9 => 7, 11, "n" => "nutty");
$b = array(9, "d" => "ditty", "b" => "bratty", "a" => null, 10, 13);
$c = array_key_diff ($a, $b, array(5 => 6));
?>

$c is then equivalent to array('c' => 'catty', 6 => 11, 'n' => 'nutty')

Csaba Gabor from New York
up
7
Anonymous
7 years ago
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;
}
?>
up
3
gilthans at NOgmailSPAM dot com
7 years ago
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--;
       
$arr1 = array_diff_once($arr1, func_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.
up
4
Colin
8 years ago
Undocumented return:  it appears this will return NULL if an error occurs (e.g., an argument is not an array) and is not caught.

<?
@array_diff(NULL, array(1));
@
array_diff(array(1), NULL);
@
array_diff();
?>

All return NULL.  (Note the "@")
up
3
doug at NOSPAM dot thrutch dot co dot uk
8 years ago
After spending half an hour scratching my head wondering why this function wasn't working I realised I had the arguments the wrong way round!

I needed to remove the contents of $array1 from $array2 so I tried:

<?php
$diff   
= array_diff($members1, $members2);
?>

WRONG!! A quick swap around and things worked smoothly...

<?php
$diff   
= array_diff($members2, $members1);
?>

Hope this saves someone a bit of bother
up
4
Simon Riget at paragi.dk
8 years ago
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.
up
3
ballestermendez at gmail dot com
2 years ago
If the element number returned is 0, this function NOT return a valid array, return NULL.
up
1
Tim Trefren
6 years ago
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;
    }
?>
up
1
kitchin
7 years ago
Until recently, the description said:
"array_diff() returns an array containing all the values of array1 that are not present in any of the other arguments. Note that keys are preserved."

Now it says:
"Compares array1 against array2 and returns the difference."

Now it's not clear what the optional arguments after the first two do.  Also, the difference is not symmetric in its arguments (that is array_intersect).
up
3
Anonymous
10 years ago
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);
?>
up
2
michiel thalen
2 years ago
The fact that it will use the string representation causes alot of problems with php 5.4.

When you will have an array inside your elements, it will throw a notice error.
It will throw huge amounts of notices depending on how many items you have.

The same problem you will notice when checking with objects inside your array. It will cause catchable fatal errors.
This is also the case in php 5.3

I'm going to send a bug report, because I think php should handle this.
up
2
firegun at terra dot com dot br
5 years ago
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;
}
?>
up
2
tim at php dot user
7 years ago
The description is wrong, array_diff() returns an array consisting of all elements in $array1 that are not in $array2. The example shows this.

Thats how it works on my php anyway.
up
2
Viking Coder
8 years ago
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
)
up
1
eugeny dot yakimovitch at gmail dot com
3 years ago
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)
up
1
merlinyoda at dorproject dot net
6 years ago
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)
}
?>
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1
MD dot ABU SAYEM=>sayem at asterisbd dot com
4 months ago
//array_diff function compare first array against all of the array and return the elements with index that are not present in either of the array.
<?php
$array1
= array("a" => "green", "red", "c"=>"blue", "red","cyan",2,3,"white");
$array2 = array("b" => "green", "yellow", "red");
$array3 = array("b" => "green", "yellow", "white",4);
$array4 = array("b" => "green", "yellow", "blue",2);
$result = array_diff($array1, $array2,$array3,$array4);
echo
"<pre>";
print_r($result);
?>
//outputs
Array
(
    [3] => cyan
    [5] => 3
)
up
0
wladimir camargo
3 years ago
This is my simple function do compare two arrays. It adds the deleted values from the original array.

<?php
function array_diff_($old_array,$new_array) {
        foreach(
$new_array as $i=>$l){
                if(
$old_array[$i] != $l){
                       
$r[$i]=$l;
                }
        }

       
//adding deleted values
       
foreach($old_array as $i=>$l){
                if(!
$new_array[$i]){
                       
$r[$i]="";
                }
        }
        return
$r;
}
?>
up
1
Jappie
8 years ago
Sorry for the bug in my last comment (probably rightfully removed by the admins).
If you want to compare more than 2 arrays, or don't know how many arrays need to be compared, this is your function:

<?php
# An extention to array_diff:
# It returns an array of all values not present in all arrays given. If '$strict' is true,
# it returns all values not present or not in the same order in all arrays given. The
# arrays to compare must be placed in another array, which is used as argument '$arrays'.
# Returns false if the '$arrays' is invalid.
function array_rdiff ($arrays, $strict = false) {
   
# check if argument is valid.
   
if (!is_array ($arrays))
        return
false;
    foreach (
$arrays as $array)
        if (!
is_array ($array))
            return
false;

   
# set working variables
   
$diff    = array ();
   
$amount  = count ($arrays);
   
$needles = array_shift ($arrays);

   
# compare
   
for ($n = 0; $n < $amount; $n++) {
        for (
$m = 0; $needles[$m]; $m++) {
           
$found     = true;
           
$positions = array ($m);
            foreach (
$arrays as $haystack) {
                if ((
$pos = array_search ($needles[$m], $haystack)) === false)
                   
$found = false;
                if (
$strict)
                   
$positions[] = $pos;
            }
            if (!
$found)
               
$diff[] = $needle;
            elseif (
$strict && (count (array_unique ($positions)) > 1))
               
$diff[] = $needle;
        }
       
$arrays[] = $needles;
       
$needles  = array_shift ($arrays);
    }
    return
array_unique ($diff);
}
?>
up
0
thefrox at gmail dot com
4 years ago
Multidimensional array_diff

<?php
echo '<pre>';
$bdd['80395']= array('80396','80397','80398','777');
$folder['80395']= array('80396','80397','666','80398','154223');
$folder['80397']= array('34','35','36','45','57');

echo
'<hr>';

function
multidimensional_array_diff($a1,$a2)
{
 
$r = array();

foreach (
$a2 as $key => $second)
{
      foreach (
$a1 as $key => $first)
      {
             
            if (isset(
$a2[$key]))
            {
                foreach (
$first as $first_value)
                {
                    foreach (
$second as $second_value)
                    {
                        if (
$first_value == $second_value)
                        {
                           
$true = true;
                            break;   
                        }
                    }
                    if (!isset(
$true))
                    {
                       
                       
$r[$key][] = $first_value;
                    }
                    unset(
$true);
                }
            }
            else
            {
               
$r[$key] = $first;
            }
      }
}
  return
$r;
}
print_r(single_diff_assoc($folder,$bdd));
?>

RESULT :

Array
(
    [80395] => Array
        (
            [0] => 666
            [1] => 154223
        )

    [80397] => Array
        (
            [0] => 34
            [1] => 35
            [2] => 36
            [3] => 45
            [4] => 57
        )

)
up
0
pikiou at somethinggooglerelated dot com
4 years ago
With previous solutions handling multi-dimensional arrays or objects through serialization, if compared variables contain references at some point, these will be serialized and stand as such after the diff function.
Here is a safer solution :
<?php
function array_diff_no_cast(&$ar1, &$ar2) {
  
$diff = Array();
   foreach (
$ar1 as $key => $val1) {
      if (
array_search($val1, $ar2) === false) {
        
$diff[$key] = $val1;
      }
   }
   return
$diff;
}
?>

Example:
<?php
$referenced
= Array(1,1);
$array1 = Array(&$referenced, Array(2,3));
$array2 = Array(Array(1,1), Array(4,5));
$result = array_diff_no_cast($array1, $array2);

print_r($result);   //Outputs Array(1 => Array(2,3))
//And $referenced stands unchanged (not serialized)
?>
up
0
Anonymous
4 years ago
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
           
$new= array_values(array_diff($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
           
$new= array_values(array_diff_key($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.
up
0
asdf at asdf dot com
6 years ago
Even tough the description of this function's behavior has changed it
does not appear as tough the function's behavior has changed.  Below is some test code and its output:

<?php

    $a
= array('1','2','3','4','5');
   
$b = array('1','a','b','c','d','e');
   
$c = array('2','f','g','h','i','j');
   
   
print_r(array_diff($a, $b, $c));

?>

Array
(
    [2] => 3
    [3] => 4
    [4] => 5
)
up
0
ahigerd at stratitec dot com
7 years ago
An earlier comment suggested using array_merge() to reindex the array. While this will work, array_values() is about 30-40% faster and accomplishes the same task.
up
0
ben dot lancaster at design-ontap dot co dot uk
8 years ago
One common caveat of this function is that if the arrays match, an empty array is return, not a strict boolean. E.g.:

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

var_dump(array_diff($array1,$array2));
/*
*Returns:
* array(0) {
* }
*/
?>
up
0
pavlicic at NOSPAM dot hotmail dot com
8 years ago
<?php

// first array
$vid_player = $vm->getVideosByPlayer($player);

// second array
$vid_playlist = $vm->getVideosByPlaylist($playlist);

// this will not work...
$vid_player = array_diff($vid_player, $vid_playlist);

// but if you do this first...
$videos = array();
foreach (
$vid_player as $player )
{
    if (
$vid_playlist != null )
    {
        foreach (
$vid_playlist as $video )
        {
            if (
$player->id == $video->id )
               
$videos[] = $player;
        }
    }
}

// this will work...
$vid_player = array_diff($vid_player, $videos);

?>
The first array_diff() compares two arrays only to find out that all the objects are unique!
up
0
air at multi dot fi
8 years ago
A small thing that caused me trouble today, wich I don't see listed on this page is that array_diff keeps the placing for the uniqe values, and removes the duplicated. This gives us empty fields in the array, wich caused me a lot of trouble. The solutions was simply to use array_merge() around the array_diff.

For example:
$array1 = array('blue', 'red', 'green');
$array2 = array('red');

array_diff($array1, $array2);

Will give us:
------
Array
(
   [0] => red
   [1] =>
   [2] => green
)

But if we use:

array_merge(array_diff($array1, $array2));

We will get:
------
Array
(
   [0] => red
   [1] => green
)
up
0
white_phoenix at ru dot ru
8 years ago
To: effectpenguin at antarctida dot ru
Re: interesting effect
<?php
function arraycpy(&$target,&$array)
{
if (!
is_array($target)) {$target = array();}
foreach(
$array as $k=>$v) {if ($k != "GLOBALS") {$target[$k] = $v;}}
}
arraycpy($old,$GLOBALS);
// some actions with variables:
$homer = "beer";
arraycpy($new,$GLOBALS);
$diff = array_diff($new,$old);
var_dump($diff);
?>
array(1) {
  ["homer"]=>
  string(4) "beer"
}
Windows NT WPX_NB 5.1 build 2600 PHP/5.0.4
up
0
rafmav
9 years ago
Here is a few functions to do a fast diff between two arrays in a few lines.
You can use it with other functions described in the function array_merge : array_merge_replace from an other user, and two functions using it : array_merge_diff and array_merge_diff_reverse.
Note that the keys are preserved!
<?
// returns a two dimensions array with the deleted data
// and the added data
function array_diff_both($new,$old)
{
   
$del=array_diff_assoc($old,$new);
   
$add=array_diff_assoc($new,$old);
    return
$diff=array("del"=>$del, "add"=>$add);
}

// returns a two dimensions array with the equal data,
// deleted data and the added data
function array_diff_all($arr_new,$arr_old)
{
   
$arr_equ=array_intersect_assoc($arr_new,$arr_old);
   
$arr_del=array_diff_assoc($arr_old,$arr_new);
   
$arr_add=array_diff_assoc($arr_new,$arr_old);
    return
$diff=array("equ"=>$arr_equ, "del"=>$arr_del, "add"=>$arr_add);
}
?>
up
0
j dot j dot d dot mol at ewi dot tudelft dot nl
9 years ago
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;
  }
?>
up
0
ds2u at the hotmail dot com
11 years ago
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
up
-1
Anonymous
11 months ago
Please note that array_diff cannot compare with an undefined array. For example:

<?php
$array1
= array ("ABC", "DEF");

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

var_dump($Result);
?>

will output NULL NULL. If your script causes an undefined array (like mine did) it can be hard to find the mistake.

Greetings
up
-1
drNOSPAMtdiggersSPAMNO at hotmail dot com
11 years ago
array_diff does not have buggy behavior as described above.  The problem stems from calling array_diff() each time in the loop, therefore regererating a new array with an index always at the beginning EVERY time, so each will always pick the first entry.  This is not buggy, but in fact what you've told the program to do :)  The solution is not as much a solution, but properly instructing the program what to do!

Cheers!
TheoDiggers
up
-2
devel-takethisout-oper dot web at gmail dot com
1 year ago
Suppose you have a CMS which saves a list of phone numbers for each user. They are stored like this:

$phones['Home'] = '(555)555-1234';
$phones['Office'] = '(555)555-2222';

You only want to save to the database if the list of items has changed. Including if the ORDER of them has changed.

<?php
// Compares two arrays- keys and values (as strings) must match.
// Keys and order must be the same to be equal.
function arraysEqual($arr1, $arr2){
    if(
count($arr1) != count($arr2)){
        return(
FALSE);
    }else{
       
$arrStr1 = serialize($arr1);
       
$arrStr2 = serialize($arr2);
        if(
strcmp($arrStr1, $arrStr2)==0 ){
            return(
TRUE);
        }else{
            return(
FALSE);
        }      
    }
}
?>
up
-1
r dot kirschke at gmx dot net
11 years ago
Are you looking for a function which returns an edit script (a set of insert and delete instructions on how to change one array into another)? At least, that's what I hoped to find here, so here's some code based on http://www.cs.arizona.edu/people/gene/PAPERS/diff.ps :

<?php
function diff_rek(&$a1,&$a2,$D,$k,&$vbck)
{
$x=$vbck[$D][$k]; $y=$x-$k;
if (
$D==0)
{
  if (
$x==0) return array(array(),array());
  else
  return array(
array_slice($a1,0,$x),array_fill(0,$x,"b"));
}
$x2=$vbck[$D-1][$k+1];
$y2=$vbck[$D-1][$k-1]-($k-1);
$xdif=$x-$x2; $ydif=$y-$y2;
$l=min($x-$x2,$y-$y2);
$x=$x-$l;
$y=$y-$l;
if (
$x==$x2)
{
  
$res=diff_rek($a1,$a2,$D-1,$k+1,$vbck);
  
array_push($res[0],$a2[$y-1]);
  
array_push($res[1],"2");
   if (
$l>0)
   {
   
$res[0]=array_merge($res[0],array_slice($a2,$y,$l));
   
$res[1]=array_merge($res[1],array_fill(0,$l,"b"));
   }
}
else
{
  
$res=diff_rek($a1,$a2,$D-1,$k-1,$vbck);
  
array_push($res[0],$a1[$x-1]);
  
array_push($res[1],"1");
   if (
$l>0)
   {
   
$res[0]=array_merge($res[0],array_slice($a1,$x,$l));
   
$res[1]=array_merge($res[1],array_fill(0,$l,"b"));
   }
}
return
$res;
}

function
arr_diff(&$a1,&$a2)
{
$max=70;
$c1=count($a1);
$c2=count($a2);
$v[1]=0;
for (
$D=0; $D<=$max; $D++)
{
   for (
$k=-$D; $k<=$D; $k=$k+2)
  {
   if ((
$k==-$D) || ($k!=$D && $v[$k-1]<$v[$k+1]))
   
$x=$v[$k+1];
   else
   
$x=$v[$k-1]+1;
  
$y=$x-$k;
   while ((
$x<$c1)&&($y<$c2)&&($a1[$x]==$a2[$y]))
    {
    
$x++;
    
$y++;
    }
   
$v[$k]=$x;
    if ((
$x>=$c1)&&($y>=$c2))
   {
   
$vbck[$D]=$v;
    return
diff_rek($a1,$a2,$D,$c1-$c2,$vbck);
   };
  }
 
$vbck[$D]=$v;
};
return -
1;
}
?>

This works on arrays of all elements for which the operator "==" is defined.
arr_dif($a1,$a2) returns an array of two arrays:
$result[0] = array of elements from $a1 and $a2
$result[1] = array of chars - one for each element from $result[0]:
"1" : The corresponding element is from $a1
"2" : The corresponding element is from $a2
"b" : The correspondig element is from both source arrays
The function returns -1, when the number of different elements is greater than $max

Example:
$a1=array("hello","world");
$a2=array("good","bye","world");
=> arr_diff($a1,$a2) = array(array("hello","good","bye","world"), array("1","2","2","b"));
up
-3
pyerre
5 years ago
be careful kids, this function can be tricky
<?php
$tab1
=array(0=>"a");
$tab2=array(0=>"a",1=>"b");

print_r(array_diff($tab1,$tab2));
?>
gives
Array
(
)
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