How to get array keys in php

array_keys

Функция array_keys() возвращает числовые и строковые ключи, содержащиеся в массиве array .

Если указан необязательный параметр search_value , функция возвращает только ключи, совпадающие с этим параметром. В обратном случае, функция возвращает все ключи массива array .

Список параметров

Массив, содержащий возвращаемые ключи.

Если указано, будут возвращены только ключи, содержащие данное значение.

Определяет использование строгой проверки на равенство (===) при поиске.

Возвращаемые значения

Возвращает массив со всеми ключами array .

Примеры

Пример #1 Пример использования array_keys()

$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 ));
?>

Результат выполнения данного примера:

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

Смотрите также

• array_values() — Выбирает все значения массива
• array_key_exists() — Проверяет, присутствует ли в массиве указанный ключ или индекс
• array_search() — Осуществляет поиск данного значения в массиве и возвращает соответствующий ключ в случае удачи

Источник

array_keys

array_keys() returns the keys, numeric and string, from the array .

If a filter_value is specified, then only the keys for that value are returned. Otherwise, all the keys from the array are returned.

Parameters

An array containing keys to return.

If specified, then only keys containing this value are returned.

Determines if strict comparison (===) should be used during the search.

Return Values

Returns an array of all the keys in array .

Examples

Example #1 array_keys() example

$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 )

See Also

• array_values() — Return all the values of an array
• array_combine() — Creates an array by using one array for keys and another for its values
• array_key_exists() — Checks if the given key or index exists in the array
• array_search() — Searches the array for a given value and returns the first corresponding key if successful

User Contributed Notes 28 notes

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.

$importantKeys = array( ‘329462291595’ => null , ‘ZZ291595’ => null );

foreach( array_keys ( $importantKeys ) as $key ) echo gettype ( $key ). «\n» ;
>

?>

will return on a 64 bits system:
integer
string
?>

but on a 32 bits system:
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:

$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.

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()
)

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.

$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

—-
expected to see:
dude dude dude

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.

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:

$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

# 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’
);

Array
(
[ 0 ] => first_index
[ 1 ] => 1
[ 2 ] => 0
[ 3 ] => 4
[ 4 ] => 08
[ 5 ] => 8
[ 6 ] =>
)

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:

foreach( $array as $key => $val ) $flattenedKeysArray [] = $key ;

if( is_array ( $val ))
array_walk_keys ( $val , $key , $flattenedKeysArray );
>

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:

I wrote a function to get keys of arrays recursivelly.

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

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.

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):

$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’],

Источник

PHP array_keys() Function

The array_keys() function returns an array containing the keys.

Syntax

Parameter Values

• true — Returns the keys with the specified value, depending on type: the number 5 is not the same as the string «5».
• false — Default value. Not depending on type, the number 5 is the same as the string «5».

Technical Details

Return Value:	Returns an array containing the keys
PHP Version:	4+
Changelog:	The strict parameter was added in PHP 5.0

More Examples

Example

Using the value parameter:

Example

Using the strict parameter, false:

Example

Using the strict parameter, true:

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Источник

PHP array_keys() Function

The array_keys() function returns an array containing the keys.

Syntax

Parameter Values

• true — Returns the keys with the specified value, depending on type: the number 5 is not the same as the string «5».
• false — Default value. Not depending on type, the number 5 is the same as the string «5».

Technical Details

Return Value:	Returns an array containing the keys
PHP Version:	4+
Changelog:	The strict parameter was added in PHP 5.0

More Examples

Example

Using the value parameter:

Example

Using the strict parameter, false:

Example

Using the strict parameter, true:

COLOR PICKER

Report Error

If you want to report an error, or if you want to make a suggestion, do not hesitate to send us an e-mail:

Thank You For Helping Us!

Your message has been sent to W3Schools.

Top Tutorials

Top References

Top Examples

Get Certified

W3Schools is optimized for learning and training. Examples might be simplified to improve reading and learning. Tutorials, references, and examples are constantly reviewed to avoid errors, but we cannot warrant full correctness of all content. While using W3Schools, you agree to have read and accepted our terms of use, cookie and privacy policy.

Источник