array_keys

    (PHP 4, PHP 5, PHP 7, PHP 8)

    array_keys — Return all the keys or a subset of the keys of an array

    Description

    array_keys(array $array): array
    array_keys(array $array, mixed $filter_value, bool $strict = false): array

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

    If a filter_value is specified, then only the keys for that value are returned. Otherwise, all the keys from the array are returned.

    Parameters

    array

    An array containing keys to return.

    filter_value

    If specified, then only keys containing this value are returned.

    strict

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

    Return Values

    Returns an array of all the keys in array.

    Examples

    Example #1 array_keys() example

    <?php
    $array     = array(0 => 100, "color" => "red");
    print_r(array_keys($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

    • array_values() - Return all the values of an array
    • array_combine() - Creates an array by using one array for keys and another for its values
    • array_key_exists() - Checks if the given key or index exists in the array
    • array_search() - Searches the array for a given value and returns the first corresponding key if successful

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    User Contributed Notes 29 notes

    up
    141
    pat dot leblanc at gmail dot com
    12 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
    59
    Sven (bitcetera.com)
    18 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
    28
    Ian (maxianos at hotmail dot com)
    10 years 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
    16
    Paul Hirsch
    9 years ago
    It is worth noting that array_keys does not maintain the data-type of the keys when mapping them to a new array. This created an issue with in_array and doing a lookup on characters from a string. NOTE: my lookup $array has a full map of numbers and characters - upper and lower - to do an simple faux encryption with.

    <?php
    $array     = array(
    'e' => 'ieio'
    ,'1' => 'one'
    ,'2' => 'two'
    ,'0' => 'zero'
    );
    var_dump($array);
    $keys = array_keys($array);
    var_dump($keys);

    $string = '1e0';
    for (    $i = 0; $i < strlen($string); $i++) {
    if (    in_array($string[$i],$keys,'strict')) echo 'dude ';
    else echo     'sweet ';
    }
    ?>

    Outputs:
    array (size=4)
    'e' => string 'ieio' (length=4)
    1 => string 'one' (length=3)
    2 => string 'two' (length=3)
    0 => string 'zero' (length=4)

    array (size=4)
    0 => string 'e' (length=1)
    1 => int 1
    2 => int 2
    3 => int 0

    sweet dude sweet

    ----
    expected to see:
    dude dude dude
    up
    17
    phpnet at holodyn dot com
    10 years 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
    16
    zammit dot andrew at gmail dot com
    10 years 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
    6
    Robert C.
    8 years ago
    Keys from multi dimensional array to simple array

    Want to traverse an multi dimensional array and get the keys back in a single dimensional array? This will do the trick:

    <?php

    public function array_walk_keys($array, $parentKey = null, &$flattened_array = null)
    {
    if(!    is_array($array))
    return     $array;

    foreach(     $array as $key => $val ) {
    $flattenedKeysArray[] = $key;

    if(    is_array($val))
    array_walk_keys($val, $key, $flattenedKeysArray);
    }

    return     $flattenedKeysArray;
    }
    up
    6
    jochem
    18 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
    1
    vittorh at outlook dot com
    10 months ago
    Hello friends

    Guys in the array_keys function manual - https://www.php.net/manual/pt_BR/function.array-keys.php

    it is described that in the second search parameter " $filter_value " is defined in mixed type, however in php 7.4 to version 8.1 when passing a $filter_value of type array, the function without returning false ( empty array )

    Exemple :

    $array = ['a' => 1, 'b' => 2];

    var_dump(array_keys($array,array('a','b'))); // return array(0) { }
    var_dump(array_keys($array,array('a','b'))); // return array(0) { }
    var_dump(array_keys($array,'a')); // return array(0) { }

    Debugging the code, I believe that the description of the $filter_value parameter is confusing, as it is understood that the value of the key in the array has to be the specified value and not the content of the key
    up
    12
    el dot quick at gmail dot com
    12 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
    4
    enrique dot balleste at gmail dot com
    7 years ago
    A nice little trick to get all of the keys who have some type of value:

    $keys = array_keys($array, !null);
    up
    3
    ayyappan dot ashok at gmail dot com
    8 years ago
    Post By Sven (59892) has to be changed

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

    $rarray = array_keys($array);

    print array_shift($rarray); // first

    print array_pop($rarray); //thrid

    print array_shift($rarray); //second

    print array_pop($rarray); // no result

    Code below is not valid from 5.4.0

    print array_shift(array_keys($array)); Throws Strict Standards Error

    Sven code works fine till 5.3.29. From 5.4.0 the standards have been changed and results too differ.

    Note :
    Strict Standards : Only variables should be passed by reference

    Please have look of the code in different versions

    http://sandbox.onlinephpfunctions.com/code/24b5fddf14b635f1e37db69a7edffc2cbbed55e1

    http://sandbox.onlinephpfunctions.com/code/f695e8f81e906b4f062b66cf9b3b83b6b620464c
    up
    7
    ferrerna at gmail dot com
    15 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
    up
    4
    rodrigo at NOSPAM dot dhweb dot com dot br
    21 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 don?t 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($arvore);
    ?>
    up
    6
    sip at email dot ee
    20 years ago
    Note, that using array_key_exists() is rather inefficient. The overhead associated with calling a function makes it slower, than using isset($array[$key]), instead of array_key_exists($key, $array)
    using isset() is usually about 1.3 times faster, according to my tests.
    up
    7
    ru dot dy at gmx dot net
    18 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
    3
    Md. Abutaleb
    4 years ago
    <?php
    # array_keys() also return the key if it's boolean but the boolean will return as 1 or 0. It will return empty if get NULL value as key. Consider the following array:

    $a = array(
    "first_index" => "This is the first element",
    true => 3,
    false => 2,
    4.5 => 'Something',
    "08" => 5,
    "8" => 6,
    NULL => 'Null key'
    );

    print_r(array_keys($a));

    Array
    (
    [    0] => first_index
    [1] => 1
    [2] => 0
    [3] => 4
    [4] => 08
    [5] => 8
    [6] =>
    )

    ?>
    up
    4
    izzecold at live dot de
    12 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
    4
    Hayley Watson
    16 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
    7
    vesely at tana dot it
    18 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
    4
    creator at mindcreations dot com
    17 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
    qeremy [atta] gmail [dotta] com
    12 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
    1
    craig1231 at hotmail dot com
    12 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;
    }
    ?>
    up
    0
    webmaster [at] baz-x [dot] at
    18 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
    0
    glennh at webadept dot net
    21 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." ";
    }
    ?>
    up
    -2
    neil at 11 out of 10
    15 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
    -7
    anthony at berglas dot org
    12 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
    -14
    nodarinodo at mail dot ru
    15 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>";
    } }
    ?>
    up
    -11
    Na&#39;ven Enigma
    12 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;
    }
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