array_key_exists
cristianDOTzuddas [AT] gmailDOTcom function has to be named "array_pos" not "array_key". This one could be array_key.
Should only be used if $search_value is unique in $array (or it returns first found key).
function:
<?php
function array_key($array, $search_value)
{
return current(array_keys($array, $search_value));
}
?>
example:
<?php
$array = array('foot', 'bike', 'car', 'plane');
print_r($array);
$key = array_key($array, 'bike');
echo("\nKey\n" . $key);
?>
output:
Array
(
[0] => foot
[1] => bike
[2] => car
[3] => plane
)
Key
1
array_keys
(PHP 4, PHP 5)
array_keys — Return all the keys of an array
Description
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 #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 )
add a note
User Contributed Notesarray_keys
info at marc-gutt dot de
26-Jun-2008 05:41
26-Jun-2008 05:41
edsongarrido at gmail dot com
12-Jun-2008 03:46
12-Jun-2008 03:46
/*
*
*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/" . $csv_name . ".csv");
exit();
}
?>
caiblack (at) hotmail (*) com
29-Jan-2008 07:04
29-Jan-2008 07:04
function array_remove_assoc_key(&$my_array=array(), $my_key='') {
if(array_key_exists($my_key, $my_array)) {
unset($my_array[$my_key]);
}
return $my_array;
}
Hayley Watson
05-Oct-2007 04:43
05-Oct-2007 04:43
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)));
}
?>
linus dot norton at assertis dot co dot uk
25-Jun-2007 05:30
25-Jun-2007 05:30
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 $keys;
}
RQuadling at GMail dot com
28-Mar-2007 04:31
28-Mar-2007 04:31
If you want to remove a value from an array, then there is no direct mechanism.
The following function uses the array_keys() function to find the key(s) of the value that you want to remove and then removes the elements for that key.
I've also given some examples and the output.
<?php
/**
* array array_remove ( array input, mixed search_value [, bool strict] )
**/
function array_remove(array &$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 $a_Input;
}
?>
Beside scalar variables (integers, floats, strings, boolean), you can also use arrays as the values you want to remove.
<?php
// Results in array(8, 8.0, '8', '8.0')
array_remove(array(8, 8.0, '8', '8.0', array(8), array('8')), array(8));
// Results in array(8, 8.0, '8', '8.0', array('8'))
array_remove(array(8, 8.0, '8', '8.0', array(8), array('8')), array(8), True);
?>
creator at mindcreations dot com
20-Mar-2007 12:12
20-Mar-2007 12:12
# This function will extract keys from a multidimensional array
function multiarray_keys($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
)
master[at]request[dot]com
23-Feb-2007 01:14
23-Feb-2007 01:14
<?
// sample Array
$strArray=array(0=>"Apple",1=>"Chery");
foreach($strArray as $key=> $val){
echo $key ."-". $val[0];
}
?>
The output is
0 - Apple 1- Chery
jason at ajax dot hk
07-Feb-2007 07:30
07-Feb-2007 07:30
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--------------------
brettz9 a/- yah00 do/- com
23-Dec-2006 04:25
23-Dec-2006 04:25
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)
?>
Ray.Paseur sometimes uses GMail
21-Dec-2006 02:38
21-Dec-2006 02:38
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);
jochem
18-Feb-2006 02:13
18-Feb-2006 02:13
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) " "
Sven (bitcetera.com)
19-Dec-2005 04:43
19-Dec-2005 04:43
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));
?>
vesely at tana dot it
09-Dec-2005 11:56
09-Dec-2005 11:56
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.
alapidus
24-Nov-2005 03:07
24-Nov-2005 03:07
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);
?>
ru dot dy at gmx dot net
14-Aug-2005 07:20
14-Aug-2005 07:20
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.
alex [@T] d-sn [D@T] com / Alex Galisteo
07-Aug-2005 12:46
07-Aug-2005 12:46
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 $arr;
}
//}}}
} //endif function_exists
?>
webmaster [at] baz-x [dot] at
30-Jul-2005 01:43
30-Jul-2005 01:43
I was looking for a function that deletes either integer keys or string keys (needed for my caching).
As I didn't find a function I came up with my own solution.
I didn't find the propiest function to post to so I will post it here, hope you find it useful.
<?php
function array_extract($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.
erwin at spammij dot nl
26-Jul-2005 03:28
26-Jul-2005 03:28
//'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]]);
}
cristianDOTzuddas [AT] gmailDOTcom
07-Jul-2005 09:41
07-Jul-2005 09:41
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;
}
}
}
?>
xorithNOSPAM (at) alsherok d.o.t net
27-May-2005 06:21
27-May-2005 06:21
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)
devmnky /at\ gmail /dot\ com
10-Mar-2005 04:03
10-Mar-2005 04:03
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
{
}
steve at ukwebsystems dot com
25-Sep-2004 08:52
25-Sep-2004 08:52
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($Row['field1']) will return false, even though the key is present...
sip at email dot ee
22-Aug-2003 03:33
22-Aug-2003 03:33
Note, that using array_key_exists() is rather inefficient. The overhead associated with calling a function makes it slower, than using isset($array[$key]), instead of array_key_exists($key, $array)
using isset() is usually about 1.3 times faster, according to my tests.
rodrigo at NOSPAM dot dhweb dot com dot br
05-Feb-2003 02:39
05-Feb-2003 02:39
[Editor's note: For a complete solution to the printing of complex structures or hashes, see the PEAR::Var_Dump package: http://pear.php.net/package-info.php?pacid=103 , use "pear install Var_Dump" to get it]
This function will print all the keys of a multidimensional array in html tables.
It will help to debug when you don´t have control of depths.
<?php
function show_keys($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);
?>
michielbakker at msn dot com
13-Nov-2002 07:45
13-Nov-2002 07:45
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. :)
glennh at webadept dot net
13-Nov-2002 02:03
13-Nov-2002 02:03
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." ";
}
?>
jacob at keystreams dot com
21-Aug-2002 09:05
21-Aug-2002 09:05
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 )