array_keys

(PHP 4, PHP 5)

array_keysReturn all the keys or a subset of the keys of an array

Description

array array_keys ( array $input [, mixed $search_value [, bool $strict = false ]] )

array_keys() returns the keys, numeric and string, from the input array.

If the optional search_value is specified, then only the keys for that value are returned. Otherwise, all the keys from the input are returned.

Parameters

input

An array containing keys to return.

search_value

If specified, then only keys containing these values are returned.

strict

Determines if strict comparison (===) should be used during the search.

Return Values

Returns an array of all the keys in input.

Changelog

Version Description
5.0.0 Added the strict parameter.

Examples

Example #1 array_keys() example

<?php
$array 
= array(=> 100"color" => "red");
print_r(array_keys($array));

$array = array("blue""red""green""blue""blue");
print_r(array_keys($array"blue"));

$array = array("color" => array("blue""red""green"),
               
"size"  => array("small""medium""large"));
print_r(array_keys($array));
?>

The above example will output:

Array
(
    [0] => 0
    [1] => color
)
Array
(
    [0] => 0
    [1] => 3
    [2] => 4
)
Array
(
    [0] => color
    [1] => size
)

See Also

add a note add a note

User Contributed Notes 24 notes

up
29
Sven (bitcetera.com)
8 years ago
Here's how to get the first key, the last key, the first value or the last value of a (hash) array without explicitly copying nor altering the original array:

<?php
  $array
= array('first'=>'111', 'second'=>'222', 'third'=>'333');

 
// get the first key: returns 'first'
 
print array_shift(array_keys($array));

 
// get the last key: returns 'third'
 
print array_pop(array_keys($array));

 
// get the first value: returns '111'
 
print array_shift(array_values($array));

 
// get the last value: returns '333'
 
print array_pop(array_values($array));
?>
up
16
pat dot leblanc at gmail dot com
2 years ago
It's worth noting that if you have keys that are long integer, such as '329462291595', they will be considered as such on a 64bits system, but will be of type string on a 32 bits system.

for example:
<?php

$importantKeys
= array('329462291595' =>null, 'ZZ291595' => null);

foreach(
array_keys($importantKeys) as $key){
    echo
gettype($key)."\n";
}

?>

will return on a 64 bits system:
<?php
    integer
    string
?>

but on a 32 bits system:
<?php
    string
    string
?>

I hope it will save someone the huge headache I had :)
up
5
el dot quick at gmail dot com
2 years ago
Sorry for my english...

I wrote a function to get keys of arrays recursivelly...

<?php
   
function recursive_keys($input, $search_value = null){

       
$output = ($search_value !== null ? array_keys($input, $search_value) : array_keys($input)) ;
        foreach(
$input as $sub){
            if(
is_array($sub)){
               
$output = ($search_value !== null ? array_merge($output, recursive_keys($sub, $search_value)) : array_merge($output, recursive_keys($sub))) ;
            }
        }
        return
$output ;
    }
?>

I hope it will be usefull

Regards
up
6
vesely at tana dot it
8 years ago
The position of an element.

One can apply array_keys twice to get the position of an element from its key. (This is the reverse of the function by cristianDOTzuddas.) E.g., the following may output "yes, we have bananas at position 0".

<?php
$a
= array("banana" => "yellow", "apple" = "red");
$k = get_some_fruit();
if (isset(
$a[$k]))
{
   list(
$pos) = array_keys(array_keys($a), $k);
   print
"yes, we have {$k}s at position $pos\n";
}
?>

Not amazingly efficient, but I see no better alternative.
up
2
sip at email dot ee
10 years ago
Note, that using array_key_exists() is rather inefficient. The overhead associated with calling a function makes it slower, than using isset($array[$key]), instead of array_key_exists($key, $array)
using isset() is usually about 1.3 times faster, according to my tests.
up
3
creator at mindcreations dot com
7 years ago
This function will extract keys from a multidimensional array

<?php
function multiarray_keys($ar) {
           
    foreach(
$ar as $k => $v) {
       
$keys[] = $k;
        if (
is_array($ar[$k]))
           
$keys = array_merge($keys, multiarray_keys($ar[$k]));
    }
    return
$keys;
}
?>

Example code:

<?php
$array
= array("color" => array("1stcolor" => "blue", "2ndcolor" => "red", "3rdcolor" => "green"),
              
"size"  => array("small", "medium", "large"));

echo
"<pre>";
print_r($array);
echo
"</pre>";

echo
"<pre>";
print_r(multiarray_keys($array));
echo
"</pre>";
?>

Example output:

Array
(
    [color] => Array
        (
            [1stcolor] => blue
            [2ndcolor] => red
            [3rdcolor] => green
        )

    [size] => Array
        (
            [0] => small
            [1] => medium
            [2] => large
        )

)

Array
(
    [0] => color
    [1] => 1stcolor
    [2] => 2ndcolor
    [3] => 3rdcolor
    [4] => size
    [5] => 0
    [6] => 1
    [7] => 2
)
up
1
anthony at berglas dot org
2 years ago
It should be noted that the inverse function to keys (which converts keys to values) is array_count_values (which converts values to keys).  This is needed to use things like array_intersect_key.  Could go in several places.  Took me a while to figure it out.
up
1
izzecold at live dot de
2 years ago
<?php

/* A Function created by myself for checking multiple array keys
For Example u got an Array like $_SESSION and u wanna know if the keys 'user','pass','email' and 'type' exists.

*/

function mKeyChecker($arr,$keys=array()) {
    if(
count($keys) > 1) {
       
$valid_keys = 0;
        foreach(
$keys as $key) {
            if(
array_key_exists($key,$arr)) $valid_keys++;
        }
        if(
$valid_keys == count($keys)) {
            return
true;
        } else {
            return
false;
        }
    } else if(
count($keys) == 1) {
        if(
array_key_exists($key[0],$arr)) {
            return
true;
        } else {
            return
false;
        }
    } else {
        return
false;
    }
}

// Execution Example

if(mKeyChecker($_SESSION,array('id','user','email','type'))) {
    echo
"is!";
} else {
    echo
"not!";   
}

?>
up
1
Ian (maxianos at hotmail dot com)
5 months ago
There's a lot of multidimensional array_keys function out there, but each of them only merges all the keys in one flat array.

Here's a way to find all the keys from a multidimensional  array while keeping the array structure. An optional MAXIMUM DEPTH parameter can be set for testing purpose in case of very large arrays.

NOTE: If the sub element isn't an array, it will be ignore.

<?php
function array_keys_recursive($myArray, $MAXDEPTH = INF, $depth = 0, $arrayKeys = array()){
       if(
$depth < $MAXDEPTH){
           
$depth++;
           
$keys = array_keys($myArray);
            foreach(
$keys as $key){
                if(
is_array($myArray[$key])){
                   
$arrayKeys[$key] = array_keys_recursive($myArray[$key], $MAXDEPTH, $depth);
                }
            }
        }

        return
$arrayKeys;
    }
?>

EXAMPLE:
input:
array(
    'Player' => array(
        'id' => '4',
        'state' => 'active',
    ),
    'LevelSimulation' => array(
        'id' => '1',
        'simulation_id' => '1',
        'level_id' => '1',
        'Level' => array(
            'id' => '1',
            'city_id' => '8',
            'City' => array(
                'id' => '8',
                'class' => 'home',
            )
        )
    ),
    'User' => array(
        'id' => '48',
        'gender' => 'M',
        'group' => 'user',
        'username' => 'Hello'
    )
)

output:
array(
    'Player' => array(),
    'LevelSimulation' => array(
        'Level' => array(
            'City' => array()
        )
    ),
    'User' => array()
)
up
0
zammit dot andrew at gmail dot com
9 months ago
If an array is empty (but defined), or the $search_value is not found in the array, an empty array is returned (not false, null, or -1). This may seem intuitive, especially given the documentation says an array is returned, but I needed to sanity test to be sure:

<?php

$emptyArray
= array();
var_dump(array_keys($emptyArray,99)); // array (size=0) \ empty

$filledArray = array(11,22,33,42);
var_dump(array_keys($filledArray,99)); // array (size=0) \ empty

?>
up
0
qeremy [atta] gmail [dotta] com
2 years ago
Simple ways to prefixing arrays;

<?php
function array_keys_prefix($arr, $pref = "") {
   
$rarr = array();
    foreach (
$arr as $key => $val) {
       
$rarr[$pref.$key] = $val;
    }
    return
$rarr;
}

function
array_keys_prefix_multi($arr, $pref = "") {
   
$rarr = array();
    foreach (
$arr as $key => $val) {
       
$rarr[] = array_keys_prefix($val, $pref);
    }
    return
$rarr;
}

// $a = array("foo" => "FOO", "bar" => "BAR", "baz" => "BAZ"); // or
$a = array("foo" => "FOO", "bar" => "BAR", "baz" => array(1,2,3));
print_r(array_keys_prefix($a, "my_"));

// db fetch...
$products = array(
    array(
"id" => 1, "name" => "Foo"),
    array(
"id" => 2, "name" => "Bar")
);
print_r(array_keys_prefix_multi($products, "product_"));
?>

Array
(
    [my_foo] => FOO
    [my_bar] => BAR
    [my_baz] => Array
        (
            [0] => 1
            [1] => 2
            [2] => 3
        )

)
Array
(
    [0] => Array
        (
            [product_id] => 1
            [product_name] => Foo
        )

    [1] => Array
        (
            [product_id] => 2
            [product_name] => Bar
        )

)
up
0
neil at 11 out of 10
6 years ago
<?php

/*
* This function will return the keys of elements in the
* haystack where the value is found in array needle
*/

function array_value_intersect_keys( $array_haystack, $array_needle ){
   
$intersected = array_intersect( $array_haystack, $array_needle );
    return
array_keys( $intersected );
}

// usage

$array_haystack = array( 1 => 2, 2 => 5, 'red' => 8, 9 => 14 );

$array_needle = array( 2, 8 );

$array_keys_of_intersecting_values = array_value_intersect_keys( $array_haystack, $array_needle );

print_r( $array_keys_of_intersecting_values );
?>

returns
Array
(
    [0] => 1
    [1] => red
)
up
0
Hayley Watson
6 years ago
An alternative to RQuadling at GMail dot com's array_remove() function:

<?php
function array_remove(array $array, $value, $strict=false)
{
    return
array_diff_key($array, array_flip(array_keys($array, $value, $strict)));
}
?>
up
0
jochem
8 years ago
might be worth noting in the docs that not all associative (string) keys are a like, output of the follow bit of code demonstrates - might be a handy introduction to automatic typecasting in php for some people (and save a few headaches):

<?php
$r
= array("0"=>"0","1"=>"1","" =>"2"," "=>"3");
echo
'how php sees this array: array("0"=>"0","1"=>"1","" =>"2"," "=>"3")',"\n-----------\n";
var_dump($r); print_r($r); var_export($r);
echo
"\n-----------\n",'var_dump("0","1",""," ") = ',"\n-----------\n";
var_dump("0","1",""," ");
?>

OUTPUTS:

how php sees this array: array("0"=>"0","1"=>"1","" =>"2"," "=>"3")
-----------
array(4) {
  [0]=>
  string(1) "0"
  [1]=>
  string(1) "1"
  [""]=>
  string(1) "2"
  [" "]=>
  string(1) "3"
}
Array
(
    [0] => 0
    [1] => 1
    [] => 2
    [ ] => 3
)
array (
  0 => '0',
  1 => '1',
  '' => '2',
  ' ' => '3',
)
-----------
var_dump("0","1",""," ") =
-----------
string(1) "0"
string(1) "1"
string(0) ""
string(1) " "
up
0
ru dot dy at gmx dot net
9 years ago
I was looking for a function that simply unset a variable amout of values from a one-dimensional array by key. I ended up with this (returns the array itself if no further parameter than the array is given, false with no params - does not change the source array)

usage: array_remove(array $input [, mixed key ...])

<?php

 
function array_remove() {
    if (
$stack = func_get_args()) {
     
$input = array_shift($stack);
      foreach (
$stack as $key) {
        unset(
$input[$key]);
      }
      return
$input;
    }
    return
false;
  }

?>

Test:

<?php
  $a
= array('a'=>'fun', 'b'=>3.14, 'sub'=> array('1', '2', '3'), 'd'=>'what', 'e' => 'xample', 5 => 'x');
 
print_r($a);
 
print_r(array_remove($a, 'd', 'b', 5, 'sub'));
?>

Output:

Array
(
    [a] => fun
    [b] => 3.14
    [sub] => Array
        (
            [0] => 1
            [1] => 2
            [2] => 3
        )

    [d] => what
    [e] => xample
    [5] => x
)
Array
(
    [a] => fun
    [e] => xample
)

Hope this helps someone.
up
0
webmaster [at] baz-x [dot] at
9 years ago
I was looking for a function that deletes either integer keys or string keys (needed for my caching).
As I didn't find a function I came up with my own solution.
I didn't find the propiest function to post to so I will post it here, hope you find it useful.

<?php

function array_extract($array, $extract_type = 1)
{
    foreach (
$array as $key => $value )
    {
        if (
$extract_type == 1 && is_string($key) )
        {
           
// delete string keys
           
unset($array[$key]);
        }
        elseif (
$extract_type == 2 && is_int($key) )
        {
           
// delete integer keys
           
unset($array[$key]);
        }
    }

    return
$array;
}

?>

You can of course define constants to have a nicer look, I have chosen these: EXTR_INT = 1; EXTR_STRING = 2
EXTR_INT will return an array where keys are only integer while
EXTR_STRING will return an array where keys are only string

Have fun with it.
up
-1
edsongarrido at gmail dot com
6 years ago
/*
*
*This function will return a .csv from a given array inside the $_SESSION['my_array']
*
*$csv_name -> the name we want the csv has to
*$download -> true or false to download the csv file after done
*
*/

<?php

function createCSV($csv_name, $download) {

       
$i = 1;
       
$csv = "";

       
/* erase the old file, if it exists */
       
@unlink("../../csv/" . $csv_name . ".csv");

       
/* array is in a session variable
         * this may be useful to avoid many db queries if it is the case */
       
$my_array = $_SESSION['my_array'];

       
/* how many fields has the given array */
       
$fields = count(array_keys($my_array[0]));

       
/* extracting the titles from the array */
       
foreach(array_keys($my_array[0]) as $title)
        {
           
/* array_keys percurs the title of each vector */
           
$csv .= $title;

           
/* while it is not the last field put a semi-colon ; */
           
if($i < $fields)
               
$csv .= ";";

           
$i++;
        }

       
/* insert an empty line to better visualize the csv */
       
$csv .= chr(10).chr(13);
               
$csv .= chr(10).chr(13);

       
/* get the values from the extracted keys */
       
foreach (array_keys($my_array) as $tipo)
        {

           
$i = 1;

            foreach(
array_keys($my_array[$tipo]) as $sub)
            {

               
$csv .= $my_array[$tipo][$sub];

                if (
$i < $fields)
                   
$csv .= ";";

               
$i++;
            }

           
$csv .= chr(10).chr(13);

        }

       
/* export the csv */
       
$export_csv=fopen("../../csv/". $csv_name .".csv", "w+");
       
fwrite($export_csv, $csv);
       
fclose($export_csv);

       
/* download the csv */
       
if ($download == true)
           
header('Location:' . "../../csv/" . $csv_name . ".csv");

        exit();

    }

?>
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0
rodrigo at NOSPAM dot dhweb dot com dot br
11 years ago
[Editor's note: For a complete solution to the printing of complex structures or hashes, see the PEAR::Var_Dump package: http://pear.php.net/package-info.php?pacid=103 , use "pear install Var_Dump" to get it]

This function will print all the keys of a multidimensional array in html tables.
It will help to debug when you donīt have control of depths.

<?php
function show_keys($ar){

   echo
"<table width='100%' border='1' bordercolor='#6699CC' cellspacing='0' cellpadding='5'><tr valign='top'>";

      foreach (
$ar as $k => $v ) {

         echo
"<td align='center' bgcolor='#EEEEEE'>
           <table border='2' cellpadding='3'><tr><td bgcolor='#FFFFFF'><font face='verdana' size='1'>
              "
. $k . "
           </font></td></tr></table>"
;

           if (
is_array($ar[$k])) {
             
show_keys ($ar[$k]);
         }

         echo
"</td>";

      }

   echo
"</tr></table>";

}

// Multidimensional array ->
$arvore = array();
$arvore['1'] = array();
$arvore['1']['1.1'] = array('1.1.1', '1.1.2', '1.1.3');
$arvore['1']['1.2'] = array('1.2.1', '1.2.2', '1.2.3');
$arvore['1']['1.3'] = array('1.3.1', '1.3.2', '1.3.3');
$arvore['2'] = array();
$arvore['2']['2.1'] = array('2.1.1', '2.1.2', '2.1.3');
$arvore['2']['2.2'] = array('2.2.1', '2.2.2', '2.2.3');
$arvore['2']['2.3'] = array('2.3.1', '2.3.2', '2.3.3');
$arvore['3'] = array();
$arvore['3']['3.1'] = array('3.1.1', '3.1.2', '3.1.3');
$arvore['3']['3.2'] = array('3.2.1', '3.2.2', '3.2.3');
$arvore['3']['3.3'] = array('3.3.1', '3.3.2'=>array('3.3.2.1', '3.3.2.2'), '3.3.3');
// <-

show_keys($arvore);
?>
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0
glennh at webadept dot net
11 years ago
All the cool notes are gone from the site.

Here's an example of how to get all the variables passed to your program using the method on this page. This prints them out so you can see what you are doing.

<?php
while (list($key, $value) = each
(${"HTTP_".$REQUEST_METHOD."_VARS"}))
{
        echo
$key." = ".$value." ";
}
?>
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-1
ferrerna at gmail dot com
5 years ago
Here's a function I needed to collapse an array, in my case from a database query.  It takes an array that contains key-value pairs and returns an array where they are actually the key and value.

<?php

function array_collapse($arr, $x, $y) {
   
$carr = array();
    while (
$el = current($arr)) {
       
$carr[ $el[$x] ] = $el[$y];
       
next($arr);
    }
    return
$carr;
}

?>

Example usage (pseudo-database code):

<?php

$query
= db_query('SELECT name, value FROM properties');

$result = db_returnAll($query);

/* This will return an array like so:

[
   ['name' -> 'color', 'value' -> 'blue'],
   ['name' -> 'style', 'value' -> 'wide-format'],
   ['name' -> 'weight', 'value' -> 3.6],
   ['name' -> 'name', 'value' -> 'Waerdthing']
]

*/

$propArr = array_collapse($result, 'name', 'value');

/* Now this array looks like:

[
   ['color' -> 'blue'],
   ['style' -> 'wide-format'],
   ['weight' -> 3.6],
   ['name' -> 'Waerdthing'],

*/

?>

I found this handy for using with json_encode and am using it for my project http://squidby.com
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-1
phpnet at holodyn dot com
9 months ago
Since 5.4 STRICT standards dictate that you cannot wrap array_keys in a function like array_shift that attempts to reference the array. 

Invalid:
echo array_shift( array_keys( array('a' => 'apple') ) );

Valid:
$keys = array_keys( array('a' => 'apple') );
echo array_shift( $keys );

But Wait! Since PHP (currently) allows you to break a reference by wrapping a variable in parentheses, you can currently use:

echo array_shift( ( array_keys( array('a' => 'apple') ) ) );

However I would expect in time the PHP team will modify the rules of parentheses.
up
-1
craig1231 at hotmail dot com
2 years ago
A needed a function to find the keys which contain part of a string, not equalling a string...

<?php
function array_keys_contain($input, $search_value, $strict = false)
    {
       
$tmpkeys = array();

       
$keys = array_keys($input);

        foreach (
$keys as $k)
        {
            if (
$strict && strpos($k, $search_value) !== FALSE)
               
$tmpkeys[] = $k;
            elseif (!
$strict && stripos($k, $search_value) !== FALSE)
               
$tmpkeys[] = $k;
        }

        return
$tmpkeys;
    }
?>
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-2
Na&#39;ven Enigma
2 years ago
I was trying to figure out how to normalize an array with numerical keys.  Since I was doing for() for a lot of things, but only replacing it if the conditions were right, I wound up with off ball arrays I couldn't access.  That being said, I looked for a method of normalizing the array and couldn't find one, so I built my own.  I'm not sure how to go about making it recursive, but I didn't need that feature for my own, so I just went without recursion.

//This will take array([5] => "test1", [4] => "test2", [9] => "test3") into array([0] => "test1", [1] => "test2", [2] => "test3") so you can access it easier.
        function normalize_array($array){
          $newarray = array();
          $array_keys = array_keys($array);
          $i=0;
          foreach($array_keys as $key){
           $newarray[$i] = $array[$key];
          
          $i++;
          }
          return $newarray;
        }
up
-2
nodarinodo at mail dot ru
5 years ago
<?php
   
//It's a way to get keys from values )
   
$es = array("is My FullName"=>"nodar chkuaselidze (nodarinodo)", "You Are" => "I don't know", "Is My Friend" => "ruxadze");
    foreach(
array_values($es) as $ess){
        echo
$ess." =>";
           
    for(
$i =0; $i < count(array_keys($es, $ess)); $i++){
            echo
reset(array_keys($es, $ess))."<BR>";
        } }
?>
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