array_keys

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 :)

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));?>

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.<?phpfunction 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())

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 0sweet dude sweet ----  expected to see:dude dude dude

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?>

Keys from multi dimensional array to simple arrayWant 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;    }

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.

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) " "

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

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

A nice little trick to get all of the keys who have some type of value:$keys = array_keys($array, !null);

Post By  Sven (59892) has to be changed$array = array('first'=>'111', 'second'=>'222', 'third'=>'333');$rarray = array_keys($array);print array_shift($rarray); // firstprint array_pop($rarray); //thridprint array_shift($rarray); //secondprint array_pop($rarray); // no resultCode below is not valid from 5.4.0 print array_shift(array_keys($array)); Throws Strict Standards ErrorSven 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 referencePlease have look of the code in different versionshttp://sandbox.onlinephpfunctions.com/code/24b5fddf14b635f1e37db69a7edffc2cbbed55e1http://sandbox.onlinephpfunctions.com/code/f695e8f81e906b4f062b66cf9b3b83b6b620464c

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.<?phpfunction 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

[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);
?>

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.

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.

<?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] => )?>

<?php/* A Function created by myself for checking multiple array keysFor 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 Exampleif(mKeyChecker($_SESSION,array('id','user','email','type'))) {    echo "is!";} else {    echo "not!";    }?>

An alternative to RQuadling at GMail dot com's array_remove() function:<?phpfunction array_remove(array $array, $value, $strict=false){    return array_diff_key($array, array_flip(array_keys($array, $value, $strict)));}?>

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.

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
)

A needed a function to find the keys which contain part of a string, not equalling a string...<?phpfunction 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;    }?>

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.<?phpfunction 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 = 2EXTR_INT will return an array where keys are only integer whileEXTR_STRING will return an array where keys are only stringHave fun with it.

PHP arrays are weird. So the result of<?php$array = [    'element0',    'element1' => 'Hello World',    'element2' => 42,    'element3' => [ 'aaa', 'bbb' ],];print_r( array_keys($array) );?>is a surprising though correctArray(    [0] => 0    [1] => element1    [2] => element2    [3] => element3)Arrays in php are really ordered key value pairs where if a value is missing it will become a value with a number as key. To get the intuitive first dimension of an array use a map with function to determine if a key is in fact an index.This<?php$array_first = array_map(    fn ($key)=>        is_int($key)?$array[$key]:$key    ,    array_keys($array));print_r($array_first);?>will showArray(    [0] => element0    [1] => element1    [2] => element2    [3] => element3)However in a niche case <?php$array = [    'element0',    'element1' => 'Hello World',    'element2' => 42,    'element3' => [ 'aaa', 'bbb' ],    12 => 'I\'m a field, not a key'];?>this won't work of course and outputArray(    [0] => element0    [1] => element1    [2] => element2    [3] => element3    [4] => I'm a field, not a key)

Simple ways to prefixing arrays;<?phpfunction 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        ))

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." ";
}
?>

<?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 );?>returnsArray(    [0] => 1    [1] => red)