array_keys

add a note User Contributed Notes

jochem
18-Feb-2006 08:13


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:



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) " "

Sven (bitcetera.com)
19-Dec-2005 10:43


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));

?>

vesely at tana dot it
09-Dec-2005 05:56


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.

alapidus
24-Nov-2005 09:07


erwin at spammij dot nl, a far more efficient solution to your problem would be to use the array_map function:



<?php



$_POST = array_map('addslashes', $_POST);



?>

ru dot dy at gmx dot net
15-Aug-2005 12:20


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.

alex [@T] d-sn [D@T] com / Alex Galisteo
07-Aug-2005 05:46


My version of PHP does not support the strict parameter. Moreover, I need a function that could make other comparsion different than equals and stricktly equals.



The funcition array_keys_advanced can make the following comparsions: equal, not equal, strictly greater than, equal or greater than, strictly less than, equal or less than.



<?php

if (!function_exists('array_keys_advanced')) {

    //{{{ array_keys_advanced

    /**

     * Returns an array with the matching keys as values. A comparsion type can

     * be spcified, even if it should be a strict comparsion or not.

     * Note: It is not recursive.

     * 

     * @param    array    $input

     * @param    string   $search_value

     * @param    bool     $strict

     * @param    string   $comparison: {EQ | NEQ | GT | EGT | LT | ELT}

     * @return   Returns an array with the matching keys as values.

     * @author   alex [@T] d-sn [D@T] com // Alex Galisteo

     */

    function array_keys_advanced() {

        $nargs = func_num_args();

        $arr = array();

        $input = null;

        $search_value = null;

        $strict = (bool) false;

        $comparison  = "EQ";

        $comparsion_types = array("EQ", "NEQ", "GT", "EGT", "LT", "ELT");

        switch ($nargs) {

        case 1:

            $input = func_get_arg(0);

            return array_keys($input);

            break;

        case 2:

            $input = func_get_arg(0);

            $search_value = func_get_arg(1);

            return array_keys($input, $search_value);

            break;

        case 3:

            $input = func_get_arg(0);

            $search_value = func_get_arg(1);

            $strict = (bool) func_get_arg(2);

            $comparsion  = "EQ";

            break;

        case 4:

            $input = func_get_arg(0);

            $search_value = func_get_arg(1);

            $strict = (bool) func_get_arg(2);

            $comparsion = strtoupper((string) func_get_arg(3));

            $comparsion = (in_array($comparsion, $comparsion_types))?

                            $comparsion : "EQ";

            break;

        default:

            return $arr;

            break;

        }

        foreach ($input as $key => $val) {

            if ($strict) {

                if ($comparsion == "EQ" && $search_value === $val) {

                    $arr[] = $key;

                }

                elseif ($comparsion == "NEQ" && $search_value !== $val)

                    $arr[] = $key;

                elseif ($comparsion == "GT" && $search_value > $val)

                    $arr[] = $key;

                elseif ($comparsion == "EGT" && $search_value >= $val)

                    $arr[] = $key;

                elseif ($comparsion == "LT" && $search_value < $val)

                    $arr[] = $key;

                elseif ($comparsion == "ELT" && $search_value <= $val)

                    $arr[] = $key;

            } else {

                if ($comparsion == "EQ" && $search_value == $val)

                    $arr[] = $key;

                elseif ($comparsion == "NEQ" && $search_value != $val)

                    $arr[] = $key;

                elseif ($comparsion == "GT" && $search_value > $val)

                    $arr[] = $key;

                elseif ($comparsion == "EGT" && $search_value >= $val)

                    $arr[] = $key;

                elseif ($comparsion == "LT" && $search_value < $val)

                    $arr[] = $key;

                elseif ($comparsion == "ELT" && $search_value <= $val)

                    $arr[] = $key;

            }

        }

        return $arr;

    }

    //}}}

} //endif function_exists

?>

webmaster [at] baz-x [dot] at
30-Jul-2005 06:43


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.

erwin at spammij dot nl
26-Jul-2005 08:28


//'This will use the array_keys function to make all $_POST values addslashed.



$post_array_keys = array_keys($_POST);



for ($g=0;$g<count($post_array_keys);$g++) {

    $_POST[$post_array_keys[$g]] = addslashes($_POST[$post_array_keys[$g]]);

}

cristianDOTzuddas [AT] gmailDOTcom
07-Jul-2005 02:41


The function extracts the key of an associative array from the position you need.



Input:

$arr = array('a'=>'first', 'b'=>'second', 'c'=>'third');

print(array_key($arr, 1));

        

Output: 'b'



<?

function array_key($arr, $pos) {

    if (!empty($arr)) {

        if ($pos===null)

            $pos = 0;

        

        $all_keys = array_keys($arr);

        unset($arr);

        

        $key = $all_keys[$pos];

        unset($all_keys);

        

        if (isset($key))

            return $key;

        else {

            unset($key);

            return null;

        }

    }

}

?>

xorithNOSPAM (at) alsherok d.o.t net
27-May-2005 11:21


Notes for steve and sip from below (wow, spanning years on these notes!)



First off, Steve is right - isset will *not* return true at all when checking for a key that has a value set to the built-in constant null. 



Sip is right in that it is faster to use isset. However, however his facts seem a bit misleading. Let me show you my console output for my test:



[Notice] Populating test array with 200000 values...

[Notice] Setting key '100000' to null for null key test.

[array_key_exists] Starting timer...

[array_key_exists] Found key 150000, time: 0.00015640

[array_key_exists] Test Complete.

[isset] Starting timer...

[isset] Found key 150000, time: 0.00008583

[isset] Test Complete.

[array_key_exists:bad_key] Starting timer...

[array_key_exists:bad_key] Did not find bad key 400000, time: 0.00009155

[array_key_exists:bad_key] Test Complete.

[isset:bad_key] Starting timer...

[isset:bad_key] Did not find bad key 400000, time: 0.00008392

[isset:bad_key] Test Complete.

[array_key_exists:null_test] Starting timer...

[array_key_exists:null_test] Found key with null value 100000, time: 0.00008392

[array_key_exists:null_test] Test Complete.

[isset:null_test] Starting timer...

[isset:null_test] Did not find key with null value 100000, time: 0.00008392

[isset:null_test] Test Complete.



Yes, that's 200,000 values. I was using an md5 of microtime() and the index, to ensure that the data was of some sort of adequate size. I had to bump up my memory_limit to do the 200,00 index test.



One thing I'd like to note is I also tried this test with 2,000 and 20,000. What I found is that the times are almost identical all the way up to 200,000. The time is in seconds.



As you can see, while there is a significant time difference between array_key_exists and isset in the first test, the time appeared to improve down the board, until it was equal with isset in the last test. You might also note that really, the time isn't too bad, not for a function that will return a more accurate result than isset.



One more test, this time 500,000 indicies:

[Notice] Populating test array with 500000 values...

[Notice] Setting key '250000' to null for null key test.

[array_key_exists] Starting timer...

[array_key_exists] Found key 375000, time: 0.00016403

[array_key_exists] Test Complete.

[isset] Starting timer...

[isset] Found key 375000, time: 0.00008011

[isset] Test Complete.

[array_key_exists:bad_key] Starting timer...

[array_key_exists:bad_key] Did not find bad key 1000000, time: 0.00007629

[array_key_exists:bad_key] Test Complete.

[isset:bad_key] Starting timer...

[isset:bad_key] Did not find bad key 1000000, time: 0.00007629

[isset:bad_key] Test Complete.

[array_key_exists:null_test] Starting timer...

[array_key_exists:null_test] Found key with null value 250000, time: 0.00007439

[array_key_exists:null_test] Test Complete.

[isset:null_test] Starting timer...

[isset:null_test] Did not find key with null value 250000, time: 0.00007629

[isset:null_test] Test Complete.



Surprisingly, the times seem a tad shorter here. This could be a result of my server though, but the fact still stands that even with an incredibly large array, the time impact isn't a huge problem with array_key_exists.



So to wrap this up:



If you care to know if a key exists, even if it's null, use array_key_exists.



If you don't want to know if a key is there if it's null, use isset.



-- JWalker (Xorith)

devmnky /at\ gmail /dot\ com
10-Mar-2005 10:03


Please note that array_keys() does not work if you're trying to search for values within multi-dimensional arrays.



For example:



$array = array("color" => array("blue", "red", "green"),

               "size"  => array("small", "medium", "large"));

print_r(array_keys($array, "blue"));



will return:

Array

{

}

steve at ukwebsystems dot com
26-Sep-2004 01:52


note to sip at email dot ee



inefficent it may be, but it detects if array keys have been defined with null values.



with the array



$Row['field1'] = null;

$Row['field2'] = 'hello';



array_key_exists('field1',$Row) will return true



isset($Row['field1']) will return false, even though the key is present...

sip at email dot ee
22-Aug-2003 08:33


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.

rodrigo at NOSPAM dot dhweb dot com dot br
05-Feb-2003 08:39


[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 dont 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);


?>

michielbakker at msn dot com
14-Nov-2002 01:45


If you receive a bunch of variables and like to change most of them (or all of them for that matter), you can do something like this: (data has been sent to a page with POST)



<?

$allKeys = array_keys($HTTP_POST_VARS);



for ($i=0;$i<count($allKeys);$i++)

{

      $$allKeys[$i] = strtoupper($HTTP_POST_VARS[$allKeys[$i]]);

}

?>



This makes caracters (a-z) uppercase. This is just one way to use it, ofcourse.



Hope this helps someone understand the way to use array_keys() or give any ideas. :)

glennh at webadept dot net
13-Nov-2002 08:03


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." ";


}


?>

jacob at keystreams dot com
21-Aug-2002 02:05


Here is a way to use array_intersect on array keys rather than values:





<?php


$a = array("apple" => "red", "banana" => "yellow");


$z = array("apple" => "green", "peach" => "orange", "banana" => "rotten");





$intersected_keys = array_intersect(array_keys($a), array_keys($z));





print_r($intersected_keys);


?>





This will print:





Array ( [0] => apple [1] => banana )

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