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PHP : Function Reference : Array Functions : array_keys

array_keys

Return all the keys of an array (PHP 4, PHP 5)
array array_keys ( array input [, mixed search_value [, bool strict]] )

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. As of PHP 5, you can use strict parameter for comparison including type (===).

Parameters

input

An array containing keys to return.

search_value

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

strict

As of PHP 5, this parameter determines if strict comparision (===) should be used during the search.

Return Values

Returns an array of all the keys in input.

Examples

Example 256. array_keys() example

copy to clipboard
<?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:

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


See Also
array_values()
array_key_exists()

Related Examples ( Source code ) » array_keys

Examples ( Source code ) » array_keys
Examples ( Source code ) » array_keys

Code Examples / Notes » array_keys

rodrigo
[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);
?>

vesely
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.

cristiandotzuddas
The function extracts the key of an associative array from the position you need.
Input:
$arr = array('a'=>'first', 'b'=>'second', 'c'=>'third');
print(array_key($arr, 1));

Output: 'b'
<?
function array_key($arr, $pos) {
if (!empty($arr)) {
if ($pos===null)
$pos = 0;

$all_keys = array_keys($arr);
unset($arr);

$key = $all_keys[$pos];
unset($all_keys);

if (isset($key))
return $key;
else {
unset($key);
return null;
}
}
}
?>

ray.paseur sometimes uses gmail
Replace a key in an associative array, preserving the original order of keys and elements:
if (!function_exists('array_combine')) { // ONLY EXISTS IN PHP5
function array_combine($keys, $values) {
if (count($keys) != count($values)) {
return false; }
foreach($keys as $key) { $array[$key] = array_shift($values); }
return $array; }
} // END IF FUNCTION EXISTS
$keys = array_keys($array);
$values = array_values($array);
foreach ($keys as $k => $v) {
if ($v == "MANAGEMENT FEE CHARGE") { $keys[$k] = "MANAGEMENT FEES"; }
}
$array = array_combine($keys, $values);

linus dot norton
RE: creator at mindcreations
I found that with my php (5.1.2) I needed to initialize $keys
function multiarray_keys($ar) {
   $keys = array();
   foreach($ar as $k => $v) {
       $keys[] = $k;
       if (is_array($ar[$k]))
           $keys = array_merge($keys, multiarray_keys($ar[$k]));
   }
   return $keys;
}

devmnky /at\ gmail /dot\ com
Please note that array_keys() does not work if you're trying to search for values within multi-dimensional arrays.
For example:
$array = array("color" => array("blue", "red", "green"),
              "size"  => array("small", "medium", "large"));
print_r(array_keys($array, "blue"));
will return:
Array
{
}

xorithnospam
Notes for steve and sip from below (wow, spanning years on these notes!)
First off, Steve is right - isset will *not* return true at all when checking for a key that has a value set to the built-in constant null.
Sip is right in that it is faster to use isset. However, however his facts seem a bit misleading. Let me show you my console output for my test:
[Notice] Populating test array with 200000 values...
[Notice] Setting key '100000' to null for null key test.
[array_key_exists] Starting timer...
[array_key_exists] Found key 150000, time: 0.00015640
[array_key_exists] Test Complete.
[isset] Starting timer...
[isset] Found key 150000, time: 0.00008583
[isset] Test Complete.
[array_key_exists:bad_key] Starting timer...
[array_key_exists:bad_key] Did not find bad key 400000, time: 0.00009155
[array_key_exists:bad_key] Test Complete.
[isset:bad_key] Starting timer...
[isset:bad_key] Did not find bad key 400000, time: 0.00008392
[isset:bad_key] Test Complete.
[array_key_exists:null_test] Starting timer...
[array_key_exists:null_test] Found key with null value 100000, time: 0.00008392
[array_key_exists:null_test] Test Complete.
[isset:null_test] Starting timer...
[isset:null_test] Did not find key with null value 100000, time: 0.00008392
[isset:null_test] Test Complete.
Yes, that's 200,000 values. I was using an md5 of microtime() and the index, to ensure that the data was of some sort of adequate size. I had to bump up my memory_limit to do the 200,00 index test.
One thing I'd like to note is I also tried this test with 2,000 and 20,000. What I found is that the times are almost identical all the way up to 200,000. The time is in seconds.
As you can see, while there is a significant time difference between array_key_exists and isset in the first test, the time appeared to improve down the board, until it was equal with isset in the last test. You might also note that really, the time isn't too bad, not for a function that will return a more accurate result than isset.
One more test, this time 500,000 indicies:
[Notice] Populating test array with 500000 values...
[Notice] Setting key '250000' to null for null key test.
[array_key_exists] Starting timer...
[array_key_exists] Found key 375000, time: 0.00016403
[array_key_exists] Test Complete.
[isset] Starting timer...
[isset] Found key 375000, time: 0.00008011
[isset] Test Complete.
[array_key_exists:bad_key] Starting timer...
[array_key_exists:bad_key] Did not find bad key 1000000, time: 0.00007629
[array_key_exists:bad_key] Test Complete.
[isset:bad_key] Starting timer...
[isset:bad_key] Did not find bad key 1000000, time: 0.00007629
[isset:bad_key] Test Complete.
[array_key_exists:null_test] Starting timer...
[array_key_exists:null_test] Found key with null value 250000, time: 0.00007439
[array_key_exists:null_test] Test Complete.
[isset:null_test] Starting timer...
[isset:null_test] Did not find key with null value 250000, time: 0.00007629
[isset:null_test] Test Complete.
Surprisingly, the times seem a tad shorter here. This could be a result of my server though, but the fact still stands that even with an incredibly large array, the time impact isn't a huge problem with array_key_exists.
So to wrap this up:
If you care to know if a key exists, even if it's null, use array_key_exists.
If you don't want to know if a key is there if it's null, use isset.
-- JWalker (Xorith)

sip
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.

steve
note to sip at email dot ee
inefficent it may be, but it detects if array keys have been defined with null values.
with the array
$Row['field1'] = null;
$Row['field2'] = 'hello';
array_key_exists('field1',$Row) will return true
isset($Row['field1']) will return false, even though the key is present...

alex @t d-sn d@t com / alex galisteo
My version of PHP does not support the strict parameter. Moreover, I need a function that could make other comparsion different than equals and stricktly equals.
The funcition array_keys_advanced can make the following comparsions: equal, not equal, strictly greater than, equal or greater than, strictly less than, equal or less than.
<?php
if (!function_exists('array_keys_advanced')) {
//{{{ array_keys_advanced
/**
* Returns an array with the matching keys as values. A comparsion type can
* be spcified, even if it should be a strict comparsion or not.
* Note: It is not recursive.
*
* @param    array    $input
* @param    string   $search_value
* @param    bool     $strict
* @param    string   $comparison: {EQ | NEQ | GT | EGT | LT | ELT}
* @return   Returns an array with the matching keys as values.
* @author   alex [@T] d-sn [D@T] com // Alex Galisteo
*/
function array_keys_advanced() {
$nargs = func_num_args();
$arr = array();
$input = null;
$search_value = null;
$strict = (bool) false;
$comparison  = "EQ";
$comparsion_types = array("EQ", "NEQ", "GT", "EGT", "LT", "ELT");
switch ($nargs) {
case 1:
$input = func_get_arg(0);
return array_keys($input);
break;
case 2:
$input = func_get_arg(0);
$search_value = func_get_arg(1);
return array_keys($input, $search_value);
break;
case 3:
$input = func_get_arg(0);
$search_value = func_get_arg(1);
$strict = (bool) func_get_arg(2);
$comparsion  = "EQ";
break;
case 4:
$input = func_get_arg(0);
$search_value = func_get_arg(1);
$strict = (bool) func_get_arg(2);
$comparsion = strtoupper((string) func_get_arg(3));
$comparsion = (in_array($comparsion, $comparsion_types))?
$comparsion : "EQ";
break;
default:
return $arr;
break;
}
foreach ($input as $key => $val) {
if ($strict) {
if ($comparsion == "EQ" && $search_value === $val) {
$arr[] = $key;
}
elseif ($comparsion == "NEQ" && $search_value !== $val)
$arr[] = $key;
elseif ($comparsion == "GT" && $search_value > $val)
$arr[] = $key;
elseif ($comparsion == "EGT" && $search_value >= $val)
$arr[] = $key;
elseif ($comparsion == "LT" && $search_value < $val)
$arr[] = $key;
elseif ($comparsion == "ELT" && $search_value <= $val)
$arr[] = $key;
} else {
if ($comparsion == "EQ" && $search_value == $val)
$arr[] = $key;
elseif ($comparsion == "NEQ" && $search_value != $val)
$arr[] = $key;
elseif ($comparsion == "GT" && $search_value > $val)
$arr[] = $key;
elseif ($comparsion == "EGT" && $search_value >= $val)
$arr[] = $key;
elseif ($comparsion == "LT" && $search_value < $val)
$arr[] = $key;
elseif ($comparsion == "ELT" && $search_value <= $val)
$arr[] = $key;
}
}
return $arr;
}
//}}}
} //endif function_exists
?>

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

jason
just tested the following example on offical help, and found that the way array_keys() works have been changed
(it now correctly return all keys even through some values are identical)
<?
$array = array("blue", "red", "green", "blue", "blue");
print_r(array_keys($array, "blue"));
?>
----------------output start-------------------
Array
(
   [0] => 0
   [1] => 3
   [2] => 4
)
-----------------output end--------------------
here's my code:
[code]
<?
$array = array("blue", "red", "green", "blue", "blue","blue", "blue");
echo '<br />source array<br />';
print_r($array);
echo '<br /><br />result of array_keys() <br />';
print_r(array_keys($array));
?>
[/code]
----------------output start-------------------
source array
Array
(
   [0] => blue
   [1] => red
   [2] => green
   [3] => blue
   [4] => blue
   [5] => blue
   [6] => blue
)
result of array_keys()
Array
(
   [0] => 0
   [1] => 1
   [2] => 2
   [3] => 3
   [4] => 4
   [5] => 5
   [6] => 6
)
-----------------output end--------------------

rquadling
If you want to remove a value from an array, then there is no direct mechanism.
The following function uses the array_keys() function to find the key(s) of the value that you want to remove and then removes the elements for that key.
I've also given some examples and the output.
<?php
/**
 * array array_remove ( array input, mixed search_value [, bool strict] )
 **/
function array_remove(array &$a_Input, $m_SearchValue, $b_Strict = False) {
$a_Keys = array_keys($a_Input, $m_SearchValue, $b_Strict);
foreach($a_Keys as $s_Key) {
unset($a_Input[$s_Key]);
}
return $a_Input;
}
?>
Beside scalar variables (integers, floats, strings, boolean), you can also use arrays as the values you want to remove.
<?php
// Results in array(8, 8.0, '8', '8.0')
array_remove(array(8, 8.0, '8', '8.0', array(8), array('8')), array(8));
// Results in array(8, 8.0, '8', '8.0', array('8'))
array_remove(array(8, 8.0, '8', '8.0', array(8), array('8')), array(8), True);
?>

michielbakker
If you receive a bunch of variables and like to change most of them (or all of them for that matter), you can do something like this: (data has been sent to a page with POST)
<?
$allKeys = array_keys($HTTP_POST_VARS);
for ($i=0;$i<count($allKeys);$i++)
{
     $$allKeys[$i] = strtoupper($HTTP_POST_VARS[$allKeys[$i]]);
}
?>
This makes caracters (a-z) uppercase. This is just one way to use it, ofcourse.
Hope this helps someone understand the way to use array_keys() or give any ideas. :)

ru dot dy
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.

webmaster
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.

sven bitcetera.com
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));
?>

jacob
Here is a way to use array_intersect on array keys rather than values:
<?php
$a = array("apple" => "red", "banana" => "yellow");
$z = array("apple" => "green", "peach" => "orange", "banana" => "rotten");
$intersected_keys = array_intersect(array_keys($a), array_keys($z));
print_r($intersected_keys);
?>
This will print:
Array ( [0] => apple [1] => banana )

alapidus
erwin at spammij dot nl, a far more efficient solution to your problem would be to use the array_map function:
<?php
$_POST = array_map('addslashes', $_POST);
?>

brettz9 a/- yah00 do/- com
Devmnky states that array_keys() doesn't work with multi-dimensional arrays. While it is true (as from his example), that array_keys does not recursively traverse the array for keys, one still can reference (or search for keys within) specific arrays within the array:
<?php
$array = array("color" => array("blue", "red", "green"), "size" => array("small", "medium", "large"));
print_r(array_keys($array['color'], "blue")); // Correctly returns Array ( [0] => 0 )  (i.e., a new array starting at key 0, referring to the key of "blue" within the "color" array: 0)
?>

hayley watson
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)));
}
?>

glennh
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." ";
}
?>

erwin
//'This will use the array_keys function to make all $_POST values addslashed.
$post_array_keys = array_keys($_POST);
for ($g=0;$g<count($post_array_keys);$g++) {
$_POST[$post_array_keys[$g]] = addslashes($_POST[$post_array_keys[$g]]);
}

master
<?
// sample Array
$strArray=array(0=>"Apple",1=>"Chery");
foreach($strArray as $key=> $val){
echo $key ."-". $val[0];
}
?>
The output is
0 - Apple 1- Chery

creator
# This function will extract keys from a multidimensional array
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:
$array = array("color" => array("1stcolor" => "blue", "2ndcolor" => "red", "3rdcolor" => "green"),
              "size"  => array("small", "medium", "large"));
echo "<pre>";
print_r($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
)

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array_change_key_case
array_chunk
array_combine
array_count_values
array_diff_assoc
array_diff_key
array_diff_uassoc
array_diff_ukey
array_diff
array_fill_keys
array_fill
array_filter
array_flip
array_intersect_assoc
array_intersect_key
array_intersect_uassoc
array_intersect_ukey
array_intersect
array_key_exists
array_keys
array_map
array_merge_recursive
array_merge
array_multisort
array_pad
array_pop
array_product
array_push
array_rand
array_reduce
array_reverse
array_search
array_shift
array_slice
array_splice
array_sum
array_udiff_assoc
array_udiff_uassoc
array_udiff
array_uintersect_assoc
array_uintersect_uassoc
array_uintersect
array_unique
array_unshift
array_values
array_walk_recursive
array_walk
array
arsort
asort
compact
count
current
each
end
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in_array
key
krsort
ksort
list
natcasesort
natsort
next
pos
prev
range
reset
rsort
shuffle
sizeof
sort
uasort
uksort
usort
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