array_intersect

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nthitz at gmail dot com
09-Jun-2006 12:09


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 11:42


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 10:54


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
11-Jun-2005 04:11


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
19-May-2005 02:19


$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 11:04


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 08:34


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 09:27


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 12:33


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
10-Jan-2004 05:11


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
10-Dec-2003 02:49


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 09:35


array_intersect($array1, $array2);

returns the same as:

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

"inerte" is my hotmail.com username
27-Jun-2003 06:50


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 07:54


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.

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