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 ( $result , ‘name’ , ‘value’ );
/* Now this array looks like:
[[‘color’ -> ‘blue’],
[‘style’ -> ‘wide-format’],
[‘weight’ -> 3.6],
[‘name’ -> ‘Waerdthing’],
Printing array keys and values with PHP
Being able to quickly or efficiently get the keys from an array which is most likely an API call is great. You can see what data exists which may not be clear in the docs (if they exist).
Here is a method with PHP to print out an array keys and values, you can even shape the loop to create a CREATE TABLE query using the keys for column names or even creating an INSERT query.
This example i am using the Reddit API, this is a multi dimensional array and you can see for the foreach i further define the row for which i want to get the keys and values for.
Printing array keys & values
The basic code with no formatting or style is:
[0][‘data’][‘children’][0][‘data’] points to the part with the keys i am after. Load up the http://www.reddit.com/r/pics/c1wqkk.json call in a json formatter to see multi dimensions to this call.If you run the code above you will notice a few errors for trying to parse arrays, that is because there is still another layer (dimension) you can go into. However these are mostly always empty for this call.
The booleans also do not get displayed (true and false), nor empty strings (“”).
Formatting and adding style
To add some formatting to display the values accurately for their type here is an added function plus a little bit of CSS to make readability better:
body < background: #0b1034; >p < color: #eca835; display: inline; >.key < color: #9f8fe2; >.value elseif (is_null($var)) < return "NULL"; >elseif ($var === '') < return '""'; >elseif ($var === true) < return 'true'; >elseif ($var === false) < return 'false'; >else < return $var; >> $data = json_decode(file_get_contents("http://www.reddit.com/r/pics/c1wqkk.json"), true); foreach ($data[0]['data']['children'][0]['data'] as $key => $value) < echo "$key
:
" . format_value_type($value) . "
"; >