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array_intersect

(PHP 4 >= 4.0.1, PHP 5)

array_intersect — 计算数组的交集

说明

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

array_intersect() 返回一个数组，该数组包含了所有在 array1 中也同时出现在所有其它参数数组中的值。注意键名保留不变。

Example #1 array_intersect() 例子

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

这使得 $result 成为： 

Array
(
    [a] => green
    [0] => red
)

Note: 两个单元仅在 (string) $elem1 === (string) $elem2 时被认为是相同的。也就是说，当字符串的表达是一样的时候。

参见 array_intersect_assoc()，array_diff() 和 array_diff_assoc()。

数组 函数
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PHP手册 - N: 计算数组的交集

用户评论:

gineko at o2 dot pl (19-Mar-2012 05:43)

array_intersect changes items values .. built-in function should be replaced with Yours code

dml at nm dot ru (20-May-2011 01:06)

The built-in function returns wrong result when input arrays have duplicate values.
Here is a code that works correctly:

<?php
function array_intersect_fixed($array1, $array2) {
    $result = array();
    foreach ($array1 as $val) {
      if (($key = array_search($val, $array2, TRUE))!==false) {
         $result[] = $val;
         unset($array2[$key]);
      }
    }
    return $result;
}
?>

faharanik (30-Jun-2010 03:30)

Here's my approach to intersection returning only the values present in all the arrays.
Note that each array must not contain duplicate values.
I don't know how effective it actually is, but perhaps it could help.

<?php
// $arrays - Array of arrays to intersect.

function calculate_intersection($arrays)
    {
    $intersection = Array();
               
    for($checked_item = 0; $checked_item < count($arrays[0]); $checked_item++)
        {
        $occurrence = 1;
       
        for($compared_array = 1; $compared_array < count($arrays); $compared_array++)
            {           
            for($compared_item = 0; $compared_item < count($arrays[$compared_array]); $compared_item++)
                {
                if($arrays[0][$checked_item] == $arrays[$compared_array][$compared_item])
                    {
                    $occurrence++;

                    if($occurrence == count($arrays))
                        {
                        $intersection[] = $arrays[0][$checked_item];
                        }
                    }
                }
            }
        }
   
    return $intersection;
    }
?>

Yohann (12-Apr-2010 12:36)

I used array_intersect in order to sort an array arbitrarly:

<?php
$a = array('one', 'two', 'three', 'four', 'five', 'six', 'seven', 'height', 'nine', 'ten');
$b = array('four', 'one', 'height', 'five')
var_dump(array_intersect($a, $b);
?>

will output:

0 => 'one'
1 => 'four'
2 => 'five'
3 => 'height'

i hope this can help...

james -at- bandit.co -dot- nz (08-Apr-2010 02:07)

I needed an array_intersect that would delete the intersecting values from the original array. Voila:

<?php
// array_intersect that splits the needle array into two - one filled with "intersected" results, and one filled with the remainder
function array_intersect_split(&$needle, $haystack, $preserve_keys = false) {
    if(!is_array($needle) || !is_array($haystack)) return false;
    $new_arr = array();
    foreach($needle as $key => $value) {
        if(($loc = array_search($value, $haystack))!==false) {
            if(!$preserve_keys) $new_arr[] = $value;
            else $new_arr[$key] = $value;
            unset($needle[$key]);
        }
    }
    return $new_arr;
}
?>

189780 at gmail dot com (02-Jan-2010 03:26)

Actually array_intersect finds the dublicate values, here is my approach which is 5 times faster than built-in function array_intersect().. Give a try..

<?php
function my_array_intersect($a,$b)
{
        for($i=0;$i<sizeof($a);$i++)
        {
                $m[]=$a[$i];
        }
        for($i=0;$i<sizeof($a);$i++)
        {
                $m[]=$b[$i];
        }
        sort($m);
        $get=array();
        for($i=0;$i<sizeof($m);$i++)
        {
                if($m[$i]==$m[$i+1])
                $get[]=$m[$i];
        }
        return $get;
}
?>

Bar?? ?UHADAR
189780@gmail.com

Shawn Pyle (13-Aug-2009 05:29)

array_intersect handles duplicate items in arrays differently. If there are duplicates in the first array, all matching duplicates will be returned. If there are duplicates in any of the subsequent arrays they will not be returned.

<?php
array_intersect(array(1,2,2),array(1,2,3)); //=> array(1,2,2)
array_intersect(array(1,2,3),array(1,2,2)); //=> array(1,2)
?>

gary (21-Jun-2009 08:57)

i wrote this one to get over the problem i found in getting strings intersected instead of arrays as there is no function in php.

<?php
function matched_main_numbers($string, $string2)
{
$string = "04 16 17 20 29";
$arr1 = explode(" ", $string);

$string2 = "45 34 04 29 16";
$arr2 = explode(" ", $string2);

$array = array_intersect($arr1, $arr2);
$comma_separated = implode($array);

$str = $comma_separated;

$balls = "$comma_separated";
$matched_balls = chunk_split($balls,2," ");
$matched_balls =" $matched_balls";

$number_of_matched_main_balls = strlen($str);
$number_of_matched_main_balls = ($number_of_matched_main_balls/2);
$numbers = "You matched $number_of_matched_main_balls main balls";

return $numbers;
       
}
?>

Oto Brglez (10-Mar-2009 03:02)

If you wish to create intersection with arrays that are empty. Than the result of intersection is empty array.

If you wish to change this. I sugest that you do this.
It simply "ignores" empty arrays. Before loop use 1st array.

<?php

$a = array();
$a[] = 1;
$a[] = 2;
$a[] = 3;

$b = array();
$b[] = 4;
$b[] = 5;
$b[] = 1;

$c = array();
$c[] = 1;
$c[] = 5;
$d = array();

$kb=array('a','b','c','d');

$out = $a;
foreach($kb as $k){
    if(!empty(${$k})) $out = array_intersect($out,${$k});
};
print_r($out);
// The result is array

// The result is empty array
print_r(array_intersect($a,$b,$c,$d));

?>

karl at libsyn dot com (30-Jan-2009 05:58)

Given a multidimensional array that represents AND/OR relationships (example below), you can use a recursive function with array_intersect() to see if another array matches that set of relationships. 

For example: array( array( 'red' ), array( 'white', 'blue' ) ) represents "red OR ( white AND blue )".  array( 'red', array( 'white', 'blue' ) ) would work, too, BTW.

If I have array( 'red' ) and I want to see if it matches the AND/OR array, I use the following function.  It returns the matched array,
but can just return a boolean if that's all you need:

<?php
$needle = array( array( 'red' ), array( 'white', 'blue' ) );
$haystack = array( 'red' );

function findMatchingArray( $needle, $haystack ) {
    foreach( $needle as $element ) {
        $test_element = (array) $element;
        if( count( $test_element ) == count( array_intersect( $test_element, $haystack ) ) ) {
            return $element;
        }

    }
    return false;
}
?>

Pretty tough to describe what I needed it to do, but it worked.  I don't know if anyone else out there needs something like this, but hope this helps.

Esfandiar -- e.bandari at gmail dot com (10-Aug-2008 08:44)

Regarding array union:  Here is a faster version array_union($a, $b)

But it is not needed!  See below.

<?php
                                        //  $a = 1 2 3 4
    $union =                            //  $b =   2   4 5 6
        array_merge(
            $a,   
            array_diff($b, $a)          //               5 6
        );                              //  $u = 1 2 3 4 5 6
?>

You get the same result with $a + $b.

N.B. for associative array the results of $a+$b and $b+$a are different, I think array_diff_key is used.

Cheers, E

stuart at horuskol dot co dot uk (07-Jul-2008 11:57)

A clearer example of the key preservation of this function:

<?php

$array1 = array(2, 4, 6, 8, 10, 12);
$array2 = array(1, 2, 3, 4, 5, 6);

var_dump(array_intersect($array1, $array2));
var_dump(array_intersect($array2, $array1));

?>

yields the following:

array(3) {
  [0]=> int(2)
  [1]=> int(4)
  [2]=> int(6)
}

array(3) {
  [1]=> int(2)
  [3]=> int(4)
  [5]=> int(6)
}

This makes it important to remember which way round you passed the arrays to the function if these keys are relied on later in the script.

Malte (10-Feb-2008 06:34)

Extending the posting by Terry from 07-Feb-2006 04:42:

If you want to use this function with arrays which have sometimes the same value several times, it won't be checked if they're existing in the second array as much as in the first.
So I delete the value in the second array, if it's found there:

<?php
$firstarray = array(1, 1, 2, 3, 4, 1);
$secondarray = array(4, 1, 6, 5, 4, 1);

//array_intersect($firstarray, $secondarray): 1, 1, 1, 4

foreach ($firstarray as $key=>$value){
    if (!in_array($value,$secondarray)){
        unset($firstarray[$key]);
    }else{
        unset($secondarray[array_search($value,$secondarray)]);
    }
}

//$firstarray: 1, 1, 4

?>

aaron (17-Dec-2006 05:36)

this one will work with associative arrays.  also an overwrite function to only replace those elements in the first array.

<?php

function array_union()
{
    if (func_num_args() < 2) { return; }
    $arrays = func_get_args();
    $outputArray = array_shift($arrays);
    $remaining = count($arrays);
    for ($i=0; $i<$remaining; $i++)
    {
        $nextArray = $arrays[$i];
        foreach ($nextArray as $key=>$value)
        {
            $outputArray[$key] = $value;
        }
    }
    return $outputArray;
}

function array_overwrite()
{
    if (func_num_args() < 2) { return; }
    $arrays = func_get_args();
    $outputArray = array_shift($arrays);
    $remaining = count($arrays);
    for ($i=0; $i<$remaining; $i++)
    {
        $nextArray = $arrays[$i];
        foreach ($nextArray as $key=>$value)
        {
            if (array_key_exists($key, $outputArray)) {    $outputArray[$key] = $value; }
        }
    }
    return $outputArray;
}

?>

Niels (20-Sep-2006 12:53)

Here is a array_union($a, $b):

<?php
                                        //  $a = 1 2 3 4
    $union =                            //  $b =   2   4 5 6
        array_merge(
            array_intersect($a, $b),    //         2   4
            array_diff($a, $b),         //       1   3
            array_diff($b, $a)          //               5 6
        );                              //  $u = 1 2 3 4 5 6
?>

nthitz at gmail dot com (09-Jun-2006 05:09)

I did some trials and if you know the approximate size of the arrays then it would seem to be a lot faster to do this <?php array_intersect($smallerArray, $largerArray); ?> Where $smallerArray is the array with lesser items. I only tested this with long strings but I would imagine that it is somewhat universal.

terry(-at-)shuttleworths(-dot-)net (07-Feb-2006 03:42)

I couldn't get array_intersect to work with two arrays of identical objects, so I just did this:

foreach ($firstarray as $key=>$value){
    if (!in_array($value,$secondarray)){
        unset($firstarray[$key]);
    }
}

This leaves $firstarray as the intersection.

Seems to work fine & reasonably quickly.

tom p (05-Nov-2005 02:54)

If you store a string of keys in a database field and want to match them to a static array of values, this is a quick way to do it without loops:

<?

$vals = array("Blue","Green","Pink","Yellow");
$db_field = "0,2,3";

echo implode(", ", array_flip(array_intersect(array_flip($vals), explode(",", $db_field))));

// will output "Blue, Pink, Yellow"

?>

sapenov at gmail dot com (10-Jun-2005 09:11)

If you need to supply arbitrary number of arguments
to array_intersect() or other array function,
use following function:

$full=call_user_func_array('array_intersect', $any_number_of_arrays_here);

SETS INTERSECTION (18-May-2005 07:19)

$a = array(1,2,3,4,5,2,6,1);  /* repeated elements --> $a is not a set */
$b = array(0,2,4,6,8,5,7,9,2,1);  /* repeated elements --> $b is not a set */

$ua = array_merge(array_unique($a));  /* now, $a is a set */
$ub = array_merge(array_unique($b));  /* now, $b is a set */

$intersect = array_merge(array_intersect($ua,$ub));

Note: 'array_merge' removes blank spaces in the arrays.
Note: order doesn't matter.

In one line:

$intersect_a_b = array_merge(array_intersect(array_merge(array_unique($a)), array_merge(array_unique($b))));

Additions/corrections wellcome...

gRiNgO

drew at iws dot co dot nz (22-Apr-2005 04:04)

Just a handy tip.

If you want to produce an array from two seperate arrays on their intersects, here you go:

<?

$a = array("branches","E_SHOP");
$b = array("E_SHOP","Webdirector_1_0");

print join("/",array_merge(array_diff($a, $b), array_intersect($a, $b), array_diff($b, $a)));

?>

Gives you:

/branches/E_SHOP/Webdirectory_1_0

blu at dotgeek dot org (15-Oct-2004 01:34)

Note that array_intersect and array_unique doesnt work well with multidimensional arrays.
If you have, for example,

<?php

$orders_today[0] = array('John Doe', 'PHP Book');
$orders_today[1] = array('Jack Smith', 'Coke');

$orders_yesterday[0] = array('Miranda Jones', 'Digital Watch');
$orders_yesterday[1] = array('John Doe', 'PHP Book');
$orders_yesterday[2] = array('Z da Silva', 'BMW Car');

?>

and wants to know if the same person bought the same thing today and yesterday and use array_intersect($orders_today, $orders_yesterday) you'll get as result:

<?php

Array
(
    [0] => Array
        (
            [0] => John Doe
            [1] => PHP Book
        )

    [1] => Array
        (
            [0] => Jack Smith
            [1] => Coke
        )

)

?>

but we can get around that by serializing the inner arrays:
<?php

$orders_today[0] = serialize(array('John Doe', 'PHP Book'));
$orders_today[1] = serialize(array('Jack Smith', 'Coke'));

$orders_yesterday[0] = serialize(array('Miranda Jones', 'Digital Watch'));
$orders_yesterday[1] = serialize(array('John Doe', 'PHP Book'));
$orders_yesterday[2] = serialize(array('Z da Silva', 'Uncle Tungsten'));

?>

so that array_map("unserialize", array_intersect($orders_today, $orders_yesterday)) will return:

<?php

Array
(
    [0] => Array
        (
            [0] => John Doe
            [1] => PHP Book
        )

)

?>

showing us who bought the same thing today and yesterday =)

[]s

tompittlik at disfinite dot net (24-Jun-2004 02:27)

Just a small mod to ben's code to make it work properly:

<?php

if(sort(array_unique($b + $a)) === sort($b))
 // $a is legit
}

?>

This is useful for checking for illegal characters in a username.

t dot wiltzius at insightbb dot com (24-Jun-2004 05:33)

I needed to compare an array with associative keys to an array that contained some of the keys to the associative array. Basically, I just wanted to return only a few of the entries in the original array, and the keys to the entries I wanted were stored in another array. This is pretty straightforward (although complicated to explain), but I couldn't find a good function for comparing values to keys. So I wrote this relatively straightforward one:

<?php

function key_values_intersect($values,$keys) {
   foreach($keys AS $key) {
      $key_val_int[$key] = $values[$key];
      }
   return $key_val_int;
   }

$big = array("first"=>2,"second"=>7,"third"=>3,"fourth"=>5);
$subset = array("first","third");

print_r(key_values_intersect($big,$subset));

?>

This will return:

Array ( [first] => 2 [third] => 3 )

anbolb at boltblue dot com (09-Jan-2004 09:11)

This is also handy for testing an array for one of a series of acceptable elements. As a simple example, if you're expecting the query string to contain one of, say, user_id, order_id or item_id, to find out which one it is you could do this:

<?php
    $valid_ids = array ('user_id', 'item_id', 'order_id');
    if ($id = current (array_intersect ($valid_ids, array_keys ($_GET))))
    {
        // do some stuff with it
    }
    else
        // error - invalid id passed, or none at all
?>

...which could be useful for constructing an SQL query, or some other situation where testing for them one by one might be too clumsy.

ben at kazez dot com (09-Dec-2003 06:49)

To check whether an array $a is a subset of array $b, do the following:

<?php
if(array_unique($b + $a) === $b)
//...
?>

Actually, PHP ought to have a function that does this for you. But the above example works.

Alessandro Ranellucci alex at primafila dot net (16-Jul-2003 02:35)

array_intersect($array1, $array2);
returns the same as:
array_diff($array1, array_diff($array1, $array2));

"inerte" is my hotmail.com username (26-Jun-2003 11:50)

If you have a slow database query that uses JOIN, try to array_intersect() the table records.

I hung up my server countless times before using this function. Simple select from one table and put the records in an array ($records_1), then select records from any other table and put them in another array($records_2).

array_intersect() will emulate a JOIN for you.

<?php
$emulated_join = array_intersect($records_1, $records_2);
?>

Remember to test if it really offers a speed improvement, your mileage may vary (database type, hardware, version, etc...)

You could also emulate a JOIN from two text files, reading each line with the file() function.

david at audiogalaxy dot com (10-Apr-2001 12:54)

Note that array_intersect() considers the type of the array elements when it compares them.

If array_intersect() doesn't appear to be working, check your inputs using var_dump() to make sure you're not trying to intersect an array of integers with an array of strings.