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array_keys

(PHP 4, PHP 5, PHP 7)

array_keys — 返回数组中部分的或所有的键名

说明

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

array_keys() 返回 input 数组中的数字或者字符串的键名。

如果指定了可选参数 search_value，则只返回该值的键名。否则 input 数组中的所有键名都会被返回。

参数

input: 一个数组，包含了要返回的键。
search_value: 如果指定了这个参数，只有包含这些值的键才会返回。
strict: 判断在搜索的时候是否该使用严格的比较（===）。

返回值

返回 input 里的所有键。

范例

Example #1 array_keys() 例子

  <?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 ));
 ?>

以上例程会输出：

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

参见

array_values() - 返回数组中所有的值
array_key_exists() - 检查给定的键名或索引是否存在于数组中
array_search() - 在数组中搜索给定的值，如果成功则返回相应的键名

用户评论:

[#1] Paul Hirsch [2015-03-30 16:31:55]

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

[#2] Ian (maxianos at hotmail dot com) [2014-03-09 03:41:50]

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()
)

[#3] zammit dot andrew at gmail dot com [2013-11-16 04:06:50]

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 ?>

[#4] phpnet at holodyn dot com [2013-10-24 05:17:15]

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.

[#5] anthony at berglas dot org [2012-04-03 05:32:28]

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.

[#6] Na'ven Enigma [2012-03-10 07:41:14]

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;
        }

[#7] qeremy [atta] gmail [dotta] com [2012-03-05 17:50:42]

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
        )

)

[#8] izzecold at live dot de [2012-01-10 09:21:49]

<?php 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!"; } ?>

[#9] craig1231 at hotmail dot com [2011-12-22 03:41:24]

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; } ?>

[#10] el dot quick at gmail dot com [2011-09-23 08:23:22]

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

[#11] pat dot leblanc at gmail dot com [2011-08-29 14:05:43]

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 :)

[#12] ferrerna at gmail dot com [2009-01-23 09:14:15]

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

I found this handy for using with json_encode and am using it for my project http://squidby.com

[#13] nodarinodo at mail dot ru [2008-12-03 11:35:26]

<?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>"; } } ?>

[#14] neil at 11 out of 10 [2008-07-24 00:10:35]

<?php 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
)

[#15] edsongarrido at gmail dot com [2008-06-12 05:46:26]

<?php function createCSV($csv_name, $download) { $i = 1; $csv = ""; @unlink("../../csv/" . $csv_name . ".csv"); $my_array = $_SESSION['my_array']; $fields = count(array_keys($my_array[0])); foreach(array_keys($my_array[0]) as $title) { $csv .= $title; if($i < $fields) $csv .= ";"; $i++; } $csv .= chr(10).chr(13); $csv .= chr(10).chr(13); foreach (array_keys($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_csv=fopen("../../csv/". $csv_name .".csv", "w+"); fwrite($export_csv, $csv); fclose($export_csv); if ($download == true) header('Location:' . "../../csv/" . $csv_name . ".csv"); exit(); } ?>

[#16] Hayley Watson [2007-10-04 18:43:50]

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))); } ?>

[#17] creator at mindcreations dot com [2007-03-20 02:12:46]

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
)

[#18] jochem [2006-02-17 16:13:35]

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) " "

[#19] Sven (bitcetera.com) [2005-12-19 06:43:57]

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)); ?>

[#20] vesely at tana dot it [2005-12-09 01:56:35]

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.

[#21] ru dot dy at gmx dot net [2005-08-14 09:20:02]

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.

[#22] webmaster [at] baz-x [dot] at [2005-07-29 15:43:16]

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.

[#23] sip at email dot ee [2003-08-22 05:33:07]

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.

[#24] rodrigo at NOSPAM dot dhweb dot com dot br [2003-02-04 16:39:10]

[#25] glennh at webadept dot net [2002-11-13 04:03:24]

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." "; } ?>