array_keys
(PHP 4, PHP 5, PHP 7, PHP 8)
array_keys — 配列のキーすべて、あるいはその一部を返す
説明
array_keys() は、配列 array
から全てのキー (数値および文字列) を返します。
filter_value
が指定された場合、
指定した値に関するキーのみが返されます。指定されない場合は、
array
から全てのキーが返されます。
パラメータ
array
-
返すキーを含む配列。
filter_value
-
指定した場合は、この値を含むキーのみを返します。
strict
-
検索時に厳密な比較 (===) を行うかどうか。
戻り値
array
のすべてのキーを配列で返します。
例
例1 array_keys() の例
<?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));
?>
上の例の出力は以下となります。
Array ( [0] => 0 [1] => color ) Array ( [0] => 0 [1] => 3 [2] => 4 ) Array ( [0] => color [1] => size )
参考
- array_values() - 配列の全ての値を返す
- array_combine() - 一方の配列をキーとして、もう一方の配列を値として、ひとつの配列を生成する
- array_key_exists() - 指定したキーまたは添字が配列にあるかどうかを調べる
- array_search() - 指定した値を配列で検索し、見つかった場合に対応する最初のキーを返す
+add a note
User Contributed Notes 27 notes
pat dot leblanc at gmail dot com ¶
13 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 :)
Sven (bitcetera.com) ¶
19 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($array));
?>
Ian (maxianos at hotmail dot com) ¶
10 years ago
There's a lot of multidimensional array_keys function out there, but each of them only merges all the keys in one flat array.
Here's a way to find all the keys from a multidimensional array while keeping the array structure. An optional MAXIMUM DEPTH parameter can be set for testing purpose in case of very large arrays.
NOTE: If the sub element isn't an array, it will be ignore.
<?php
function array_keys_recursive($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()
)
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
zammit dot andrew at gmail dot com ¶
11 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
?>
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;
}
phpnet at holodyn dot com ¶
11 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.
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) " "
vittorh at outlook dot com ¶
1 year 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 $filter_value parameter is confusing, as it is understood that the value of the key in the array has to be the specified value and not the content of the key
el dot quick at gmail dot com ¶
13 years ago
Sorry for my english...
I wrote a function to get keys of arrays recursivelly...
<?php
function recursive_keys($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
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);
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($array)); Throws Strict Standards Error
Sven code works fine till 5.3.29. From 5.4.0 the standards have been changed and results too differ.
Note :
Strict Standards : Only variables should be passed by reference
Please have look of the code in different versions
http://sandbox.onlinephpfunctions.com/code/24b5fddf14b635f1e37db69a7edffc2cbbed55e1
http://sandbox.onlinephpfunctions.com/code/f695e8f81e906b4f062b66cf9b3b83b6b620464c
ferrerna at gmail dot com ¶
15 years ago
Here's a function I needed to collapse an array, in my case from a database query. It takes an array that contains key-value pairs and returns an array where they are actually the key and value.
<?php
function array_collapse($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
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);
?>
sip at email dot ee ¶
21 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.
ru dot dy at gmx dot net ¶
19 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.
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] =>
)
?>
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!";
}
?>