array_key_exists

(PHP 4 >= 4.0.7, PHP 5, PHP 7)

array_key_exists — Checks if the given key or index exists in the array

Description

bool array_key_exists ( mixed $key , array $array )

array_key_exists() returns TRUE if the given key is set in the array. key can be any value possible for an array index.

Parameters

key: Value to check.
array: An array with keys to check.

Return Values

Returns TRUE on success or FALSE on failure.

Examples

Example #1 array_key_exists() example


<?php
$search_array = array('first' => 1, 'second' => 4);
if (array_key_exists('first', $search_array)) {
    echo "The 'first' element is in the array";
}
?>

Example #2 array_key_exists() vs isset()

isset() does not return TRUE for array keys that correspond to a NULL value, while array_key_exists() does.


<?php
$search_array = array('first' => null, 'second' => 4);

// returns false
isset($search_array['first']);

// returns true
array_key_exists('first', $search_array);
?>

Notes

Note:
For backward compatibility reasons, array_key_exists() will also return TRUE if key is a property defined within an object given as array. This behaviour should not be relied upon, and care should be taken to ensure that array is an array.

To check whether a property exists in an object, use property_exists().

User Contributed Notes

Nik Tang

4 years ago


If you want to take the performance advantage of isset() while keeping the NULL element correctly detected, use this:

if (isset(..) || array_key_exists(...))
{
...
}

Benchmark (100000 runs):
array_key_exists() : 205 ms
is_set() : 35ms
isset() || array_key_exists() : 48ms

Note: 
The code for this check is very fast, so you shouldn't warp the code into a single function like below, because the overhead of calling a function dominates the overall performance.

function array_check(...)
{
    return (isset(..) || array_key_exists(...))
}

Venkata Subbaraju

5 months ago


array_key_exists perfect for $_GET .

As there will be browser level restriction on length of URL , number of keys in $_GET global variable will be very limited . So array_key_exists will not cause any performance overhead in this context . isset function can be conveniently ignored while handling $_GET variable.

But for $_POST , the max array size has to be configure in server PHP configuration . So cannot rely on array_key_exists for $_POST if max array size is not optimized . 

Here is an example with array_key_exists switching between content-types :

if(array_key_exists('format',$_GET))
{
              if($_GET['format']=="json")
              { 
                      header('Content-Type: application/json');
              }
              else{
                     //handle any other format whitelisted for the application
              }
}
else {
               error_log("format parameter missing . using default html format");
               header('Content-Type: text/html');
}

ellert at vankoperen dot nl

1 year ago


While working with large JSON datastructures I encountered an increasing need to check the presence of certain data all over the place.
This led to the function below that lets you simply access the data, and returns it if available, null if not.
Note that it uses a variable number of parameters, you can go as deep into a nested structure as you want.

<?php
function safe_array_access($ar){
    $numargs = func_num_args();
    $arg_list = func_get_args();
    $aritterator = $ar;
    for($i = 1; $i < $numargs; $i++){
        if (isset($aritterator[$arg_list[$i]]) || array_key_exists($arg_list[$i], $aritterator)){
            $aritterator = $aritterator[$arg_list[$i]];
        }else{
            return(false);
        }
    }
    return($aritterator);
}
?>
Usage:
Instead of  $a['b']['c'] use safe_array_access($a, 'b', 'c');

mankyd at gmail dot com

7 years ago


You'll notice several notes on this page stating that isset() is significantly faster than array_key_exists(). This may be true except for one small hitch. isset() will return false for arrays keys that have there value set to NULL, which is therefore not entirely accurate.

Example:

<?php
$foo = array();
$foo['bar'] = NULL;

var_dump(isset($foo['bar']));
var_dump(array_key_exists('bar', $foo));
?>

will output:
bool(false)
bool(true)

Be aware of this!

mc dot watras at gmail dot com

1 year ago


array_key_exists doesn't work with objects implementing ArrayAccess interface. It also ignores possible __get() method in such objects, despite the fact it accepts object as a second parameter. It works only with 'real' properties.

<?php
class A implements ArrayAccess {
    public $data;
    public function offsetExists($offset) {
        return isset($this->data[$offset]);
    }
    public function __get($property) {
        return $this->data[$property];
    }
}

$a = new A();
$a->data['somekey'] = 1;
var_dump(array_key_exists('somekey', $a)); // returns false
var_dump(array_key_exists('data', $a));  // returns true
?>

Anonymous

4 years ago


I just want to note that array_key_exists() can be extremely slow for large (>200 keys) arrays.  Use isset($array($key)) instead!  My program ran in 3 minutes instead of 2 hours after switching to isset()!

tmont

8 years ago


The argument of array_key_exists() vs. isset() came up in the workplace today, so I conducted a little benchmark to see which is faster:

<?php
    // one-dimensional arrays
    $array = array_fill(0,50000,'tommy is the best!');
    $arraykeyexists_result = array();

    $start = microtime(true);
    for ($i = 0; $i < 100000; $i++) {
        if (array_key_exists($i,$array)) {
            $arraykeyexists_result[] = 1;
        }
        else {
            $arraykeyexists_result[] = 0;
        }
    }
    $arrtime = round(microtime(true)-$start,3);
    
    $start = microtime(true);
    for ($i = 0; $i < 100000; $i++) {
        if (isset($array[$i])) {
            $arraykeyexists_result[] = 1;
        }
        else {
            $arraykeyexists_result[] = 0;
        }
    }
    $istime = round(microtime(true)-$start,3);
    
    $totaltime = $arrtime+$istime;
    $arrpercentage = round(100*$arrtime/$totaltime,3);
    $ispercentage = round(100*$istime/$totaltime,3);    
    
    echo "array_key_exists(): $arrtime [$arrpercentage%] seconds\n";
    echo "isset():            $istime [$ispercentage%] seconds\n";

?>

On Windows, the output is similar to

array_key_exists(): 0.504 [82.895%] seconds
isset():            0.104 [17.105%] seconds

On Mac or Linux, isset() is faster but only by a factor of approximately 1.5.

webmaster at oehoeboeroe dot nl

6 years ago


The way array_key_exists handles null, float, boolean, and 'integer-representing string' keys is inconsistent in itself and, in the case of bool and float, with the way these are converted when used as array offset.

<?php
$array = array(null => 1, false => 2, true => 3, 4.6 => 4, "08" => 5, "8" => 6);
var_export($array);

echo "\nnull is " . (array_key_exists(null, $array) ? '' : 'not ') . "a key.\n";
echo 'false is ' . (array_key_exists(false, $array) ? '' : 'not ') . "a key.\n";
echo 'true is ' . (array_key_exists(true, $array) ? '' : 'not ') . "a key.\n";
echo '4.6 is ' . (array_key_exists(4.6, $array) ? '' : 'not ') . "a key.\n";
echo '"08" is ' . (array_key_exists("08", $array) ? '' : 'not ') . "a key.\n";
echo '"8" is ' . (array_key_exists("8", $array) ? '' : 'not ') . "a key.\n";
?>

Output:

array (
  '' => 1,
  0 => 2,
  1 => 3,
  4 => 4,
  '08' => 5,
  8 => 6,
)
null is a key.
false is not a key.
true is not a key.
4.6 is not a key.
"08" is a key.
"8" is a key.

Well, and you get this warning three times (on the bools and the float, but not on the null):

Warning:  array_key_exists() [function.array-key-exists]: The first argument should be either a string or an integer in /var/www/php/test.php on line 6

inker2576 at yahoo dot com

9 years ago


Further research on this has turned up that the performance problems are a known, confirmed bug in PHP 5.1.x, and have been fixed in PHP builds after September 2006.  You can find the bug report here:  http://bugs.php.net/bug.php?id=38812

However, just because it's a fixed bug doesn't really change the conclusion.  If you're writing a script and there's any chance it could be used on a PHP 5.1.x server, you should still avoid this function and use isset() or some other kind of test if you want it to run efficiently.

John

7 years ago


Here is a little function for case sensitivity to elaborate on what was said by MarkL from ##php (Freenode) and mmanning at mdanderson dot org from this page:



<?php

// Case sensitive version of array_key_exists() using preg_match()

function array_ikey_exists($key,$arr)

{

    if(preg_match("/".$key."/i", join(",", array_keys($arr))))                

        return true;

    else

        return false;

}

?>



Not that anyone else couldn't have written this, but a concept like this strengthens reusability.  :)



Also, I've been running into issues with escaping for Regex, so I decided to give something like this a shot:



<?php

function array_ikey_exists($key,$arr)

{

    $e = 0; //$key = addslashes($key);

    if(is_array($arr) && $arr !==array())

    {

        foreach($arr as $k => $v)

        {    

            if(strtolower($k) == strtolower($key))

                $e++;

        }

        if($e>0)

            return true;        

        else

            return false;

    }

    else

        return false;

}

?>



You could addslashes() to escape; it's just another approach.

wolf550e at gmail dot com

8 years ago


array_key_exists(), at least in 5.2.4, passes the array by value. I conclude this from seeing performance worsen as the array to search got bigger. isset() doesn't have this problem.

Lucknut dot xbl at googlemail dot com

8 years ago


I found this function very good to use if your want your urls like index.php?login or index.php?register
e.g.
<?php
if( array_key_exists( 'home',$_GET ) ) {
    echo "Home - its where the heart is.";
} else if( array_key_exists( 'login',$_GET ) ) {
    echo "Login code here!";
} else if( array_key_exists( 'register',$_GET ) ) {
    echo "Register code here!";
} else {
    echo "Home - its where the heart is.";
}
?>

david at madole dot net

8 years ago


Regarding performance differences between isset() and array_key_exists(), the differences may be there, but the function are not always interchangable.

Note that when $a[1] = null then isset($a[1]) == false but array_key_exists(1, $a) == true

manhon824 at gmail dot com

4 years ago


I took hours for me to debug, and I finally recognized that,

You have to reset the $array before using array_key_exists 
reset($array);
array_key_exists($needle,$array);

Or you will get no reply.

PHPEric

6 years ago


Very simple case-insensitive array_key_exists:

bool (in_array(strtolower($needle), array_map('strtolower', array_keys($haystack))))

Matt

9 years ago


mikael dot knutsson at gmail dot com:
I don't think it does, at least in PHP5?

For example, this outputs bool(false):

$ar = array ( 'outter' => array ( 'inner' => 1 ) );
var_dump(array_key_exists('inner', $ar));

So it doesn't actually check the inner array for the key 'inner'.

Rudi

4 years ago


I've got a new take on the multi key function I would like to share.

<?php 
function array_multi_key_exists(array $arrNeedles, array $arrHaystack, $blnMatchAll=true){
    $blnFound = array_key_exists(array_shift($arrNeedles), $arrHaystack);
    
    if($blnFound && (count($arrNeedles) == 0 || !$blnMatchAll))
        return true;
    
    if(!$blnFound && count($arrNeedles) == 0 || $blnMatchAll)
        return false;
    
    return array_multi_key_exists($arrNeedles, $arrHaystack, $blnMatchAll);
}
?>

Hope you'll find it usefull.

p dot allgeier at web dot de

8 months ago


If u want to check if a key exists either in the array or in any subarray try the following:

<?php

function requireKey($needle, array $array)
    {
        foreach ($array as $key => $value) {
            if ($key === $needle) return $value;
            if (is_array($value)) {
                if ($x = $this->requireKey($key, $value)) return $x;
            }
        }
        return false;
    }

?>

(( return $value for recursive array search, return true for recursive array key exists ))

diogoshaw at gmail dot com

8 years ago


this function very good to use if you need to verify many variables:

<?php
function array_key_exists_r($keys, $search_r) {
    $keys_r = split('\|',$keys);
    foreach($keys_r as $key)
    if(!array_key_exists($key,$search_r))
    return false;
    return true;
}
?>

e.g.

<?php
if(array_key_exists_r('login|user|passwd',$_GET)) {
// login
} else {
// other
}
?>

works for me, enjoy.
dg shaw.

jens dot hoevenaars at gmail dot com

5 years ago


I created this function that uses array key exist to compare a form and a table to see if something has changed.



This can be very helpfull if you need to update a table record from a form but you do not want to display all table fields.



<?php

function($data_from_db, $form_data) {

 $data = $data_from_db;

 $keys = array_keys($data);



    for($i = 0; $i < count($data); $i++) {

        if(!array_key_exists($keys[$i], $form_data)) {

            $dbobject->$keys[$i] = $data[$keys[$i]];

        } else {

            $dbobject->$keys[$i] = $form_data[$keys[$i]];

        }

    }

    return $dbobject;

}

?>



you can then use the dbobject to update the table.

eidberger at jakota dot de

8 years ago


Just wondered why array_key_exists() makes me a cpu-load of 85% while isset() only needs 35%.

Not a big thing for one time execution, but in my case it have to check 1-dimensional array with ~ 15.000 entries 100 times a second. My code checks a big array for existing entrys and updates them, if needed.

Hopes it helps somebody. Notice that on many other functions, which makes coding more comfortable at the cost of speed.

gmdebby at gmail dot com

6 years ago


A little function which take an array as keys

<?php
//note the s in the function name (keys)
function array_keys_exists($array,$keys) {
    foreach($keys as $k) {
        if(!isset($array[$k])) {
        return false;
        }
    }
    return true;
}
?>
//useful to validate a form for example
<form>
    <input type="text" name="field1" /><br />
    <input type="text" name="field2" /><br />
    <input type="text" name="field3" /><br />
    <input type="text" name="field4" /><br />
    <input type="text" name="field5" /><br />
</form>
<?php
if(!array_keys_exists($_POST,
array("field1","field2","field3","field4","field5")
)) {
    //some fields are missing, dont do anything (maybe hacking)
} else {
    //code ...
}
?>

Sandro Alves Peres

2 years ago


<?php
/*
    It also works on objects
    ***************************************
*/

class PHP
{

    private $compiler;
    protected $architecture;
    public $version;
    public $system = "Linux";
    
}

$php = new PHP();

$a = array_key_exists('compiler', $php);     # false
$b = array_key_exists('architecture', $php); # false
$c = array_key_exists('version', $php);      # true
$d = array_key_exists('system', $php);       # true

var_dump( $a, $b, $c, $d );

?>

imaginary at friend dot com

4 years ago


An even simpler case-insensitive alternative to array_key_exists():

<?php

array_key_exists(strtolower($key), array_change_key_case($search));

glitch dot mr at gmail dot com

4 years ago


As you might know, isset() is actually working like @$variable===NULL. As the result, it doesn't actually catch variables set to NULL. If you want to check if variable is set (even to NULL), you can use array_key_exists on $GLOBALS, like there.

<?php
   $me = null;
   $se = 1;
   unset($se);
// $he is not set

if(array_key_exists('me', $GLOBALS)) echo "\$me exists\n";
if(array_key_exists('se', $GLOBALS)) echo "\$se exists\n";
if(array_key_exists('he', $GLOBALS)) echo "\$he exists\n";

?>

In this case, only $me will be detected as $se was removed when code was running and $he was never set.

tech at signhere envy dot de

5 years ago


Hey, this function is able to rename a key inside an array.

If the key to be replaced doesn't exist inside the array, or the new key already exists in the array, the function will return FALSE.
Otherwise, the array with the renamed key will be returned.

Hope this will be useful for someone.
<?php
function array_rename_key($array, $key, $newkey){
    if( ! array_key_exists($key, $array) || array_key_exists($newkey, $array)) return FALSE;
    $uid = uniqid(''); //To clearly identify the Element.
    $preserve_value = $array[$key]; //Keep the Value
    $array[$key] = $uid; //Overwrite Value with ID
    $array = array_flip($array); //Flip the Array keys and values
    $array[$uid] = $newkey; //Set Value of the ID with new Key.
    $array = array_flip($array); //Everything back in Place.
    $array[$newkey] = $preserve_value;
    return $array;
}
?>

jacobsingh at gmail dot com

7 years ago


I saw some examples above for array_keys_exist() or functions to see if multiple keys exist in a given array and return false if any of them don't.

Here is a simpler way to do this:

<?php

function array_keys_exist($keys,$array) {
    if (count (array_intersect($keys,array_keys($array))) == count($keys)) {
        return true;
    }
}

$array = array ('filename' => 'myfile', 'filesize' => 1234, 'filepath' => '/tmp/myfile');
$keys = array('filename','filesize','filepath');

echo array_keys_exist($keys,$array);
//returns true

$keys[] = "somethingelse";

echo array_keys_exist($keys,$array);
//Returns false

?>

bplessingerMONKEYleapfroginteractive.com

8 years ago


I noticed that the function for recursion broke the ability to use this on objects, so I added another check to also allow it to work for objects.

<?php

function array_key_exists_r($needle, $haystack)
{
    $result = array_key_exists($needle, $haystack);
    if ($result)
        return $result;
    foreach ($haystack as $v)
    {
        if (is_array($v) || is_object($v))
            $result = array_key_exists_r($needle, $v);
        if ($result)
        return $result;
    }
    return $result;
}
?>

packard_bell_nec at hotmail dot com

8 years ago


You can check whether a variable is defined by using array_key_exists()! 
First, you may ask that no reserved array (would be called $LOCALS) is predefined in function scope (contrast to reserved array $GLOBALS in global scope. To solve it, you can use compact(). 
Then, you may ask that why property_exists() cannot be used. This is because no reserved function is predefined to create OBJECT containing variables and their values, and no reserved function is predefined to import variables into the current symbol table from an OBJECT. In addition, property_exists() breaks the naming convention of reserved function. 
Finally, I show how to check whether a variable is defined by using array_key_exists(): 
<?php
function too(){
$roo = array_key_exists('foo', compact('foo'));
echo ($roo?'1':'0').'<br/>';
$foo = null;
$roo = array_key_exists('foo', compact('foo'));
echo ($roo?'1':'0').'<br/>';
}
too();
?>
The output will be: 
0<br/>
1<br/>

php at ianco dot co dot uk

9 years ago


array_key_exists is case sensitive (at least in PHP 4.3.9). To make a case-insensitive comparison you could use strtolower on both sides.

moandsimon at btinternet dot com

6 years ago


This uses array_key_exists.



You have a multidimensional array of the form:



$rowsoriginal[] = array('field_wrkvolmin_value' => 216, 'field_wrkvolmax_value' => 1000);

$rowsoriginal[] = array('field_wrkvolmin_value' => 27, 'field_wrkvolmax_value' => 216);



Using print_r this will look like:



Array ( [0] => Array ( [field_wrkvolmin_value] => 216 [field_wrkvolmax_value] => 1000 ) [1] => Array ( [field_wrkvolmin_value] => 27 [field_wrkvolmax_value] => 216 ) )



This can be used to create a table by iterating over the rows that looks like this:



field_wrkvolmin_value          field_wrkvolmax_value

           216                                      1000

            27                                       216



when $rowsoriginal contain a fixed but unknown amount of values.



If you want to process this in an automatic way without knowing the keys etc, into a multidimensional array of the form:



$rowstemp = array('field_wrkvolmin_value' => array(216, 27), 'field_wrkvolmax_value' => array(1000, 216));



Using print_r this will look like:



Array ( [field_wrkvolmin_value] => Array ( [0] => 216 [1] => 27 ) [field_wrkvolmax_value] => Array ( [0] => 1000 [1] => 216 ) )



This can be used to iterate over the rows of a table to create a table in the form of:



field_wrkvolmin_value            216            27

field_wrkvolmax_value           1000           216



To do this you can use the following looping and conditional structure, using array_key_exists():



<?php

$rowstemp = array();

foreach ($rowsoriginal as $row) {

    foreach ($row as $key => $value) {

        if (array_key_exists($key, $rowstemp)) {

            $rowstemp[$key][] = $value;

        }

        else {

            $valuestemp = array($value);

            $rowstemp[$key] = $valuestemp;

        }

    }

}

?>

mmanning at mdanderson dot org

7 years ago


Something to keep in mind is that array_key_exists is case sensitive.  So two things I'd like to say:

1. Could there be an additional option added on to the array_key_exists command so you can specify the case to be insensitive?

2. Here is how you can do this test in one command:

   if( preg_match("/<key>/i", join(",", array_keys(<array>))) ){
      <Do something>
      }

But it would be a lot nicer to just have an additional option on the array_key_exists.  Like so:

   array_key_exists(<array>, ["i"] );

Ok - so why did this come up at all?  I wrote a routine to convert any whacky UppERcAsE kind of lettering to just be lowercase letters. (ex: FgColorS becomes fgcolors and so forth.)  So I never had to guess what the user was putting in to the program.  There were two particular items (fgColors and bgColors) which I wanted to test against.  If they were not supplied, my program would supply them.  The above was the easiest way I could come up with to do this.  :-)

Karim Ratib

7 years ago


Here's a function to return a reference to the first array element that has a given key. The code works for multidimensional arrays:

<?php
function &array_find_element_by_key($key, &$form) {
  if (array_key_exists($key, $form)) {
    $ret =& $form[$key];
    return $ret;
  }
  foreach ($form as $k => $v) {
    if (is_array($v)) {
      $ret =& array_find_element_by_key($key, $form[$k]);
      if ($ret) {
        return $ret;
      }
    }
  }
  return FALSE;
}
?>

sj-b at hotmail dot de

8 years ago


i dont like how empty() works.
an integer with value 0 or a boolean wth
value false (same like zero) counts as
empty too.

[code]function r_empty (&$check)
{
    if (!isset($check)) return true;
    if ($check == NULL) return true;
    return false;
}[/code]

that is a good replacement for
both functions for me.

serkan yersen

9 years ago


marzetti.marco,
I fixed your function it's is more optimized and working better now.

function regex_array_keys($arr, $pattern){
   $results[] = false;

   if(!is_array($arr))
       return false;

   foreach($arr as $key => $val){
         if(!is_array($key))
       if(preg_match($pattern,$key))
              array_push($results,$key);
   }

   return $results;
}

tom at edgedesigns dot org

6 years ago


The multi_array_key_exists() function posted by alishahnovin at hotmail dot com [which has since been removed] does not always return the expected result.



This modified version does.



<?php

/**

 * multi_array_key_exists function.

 * 

 * @param mixed $needle The key you want to check for

 * @param mixed $haystack The array you want to search 

 * @return bool

 */

function multi_array_key_exists( $needle, $haystack ) {

 

    foreach ( $haystack as $key => $value ) :



        if ( $needle == $key )

            return true;

        

        if ( is_array( $value ) ) :

             if ( multi_array_key_exists( $needle, $value ) == true )

                return true;

             else

                 continue;

        endif;

        

    endforeach;

    

    return false;

}



?>

mikael dot knutsson at gmail dot com

9 years ago


When dealing with multi-dimensional arrays, this function checks through all keys in the array, including the "child arrays" unlike the array_keys( array, $search ) function which would only check and return from the first level of keys.

Took me a couple of minutes to figure out what was wrong and I hope it helps some people when looking for the right function.

csaba at alum dot mit dot edu

7 years ago


In some functions cacheing can be extremely useful, and this is especially true in recursive functions, and all the more so in doubly recursive functions.  One way to effect cacheing is to have a static array in the function as shown below.  This will typically be useful when a function has one or two arguments and is heavily called.  Example:

<?php
function nk($n, $k) {
  // n choose k, ensuring integer math
  if ($k > $n-$k) $k = $n - $k;         // (n,k) = (n,n-k)
  if ($k<=1) return ($k==1) ? $n : !$k; // (n,1) = n; (n,0)=1; (n,-#) = 0

  static $aNK = array();                // caching section
  if ($aNK[$n][$k]) return $aNK[$n][$k];// if answer already computed => done

  // else compute answer, cache it, and return
  return ($aNK[$n][$k] = nk($n-1, $k) + nk($n-1, $k-1)); }

$n = 20;
$k = 9;
$nk = nk($n,$k);
print "nk($n, $k) = $nk";
?>

For functions of two arguments, using a two dimensional array seems to be faster than combining arguments a la "$n $k", and the form of testing shown above is also faster than array_key_exists.  However, to avoid the use of array_key_exists, special consideration must be given to empty values (several prior notes cover this) - the example above works because no cached value can be 0.

Csaba Gabor from Vienna

david at lostair dot com

7 years ago


It is important to realise that:

  isset($array ['index'])

Does not act the same as:

  array_key_exists('index', $array)

This is because if an array value is set to NULL

$array['index'] = NULL;

Then isset will return FALSE and array_key_exists will return TRUE.

It is important to realise this!

jakub dot lopuszanski at nasza-klasa dot pl

2 years ago


It's not mentioned directly in this spec, but implementing ArrayAccess intereface is unfortunately not enough to make array_key_exists work as expected :(
In other words array_key_exists and ArrayAccess::offsetExists is not the same thing :/

array_key_exists

Description

Parameters

Return Values

Examples

Notes

See Also

User Contributed Notes