array_reverse

(PHP 4, PHP 5)

array_reverse — 要素を逆順にした配列を返す

説明

array array_reverse ( array $array [, bool $preserve_keys ] )

array_reverse() は、array を引数とし、要素の順番を逆にした新しい配列を返します。この時、 preserve_keys が TRUE の場合はキーが保持されます。

Example#1 array_reverse() の例


<?php
$input  = array("php", 4.0, array("green", "red"));
$result = array_reverse($input);
$result_keyed = array_reverse($input, true);
?>

この例において、$result と $result_keyed は同じ要素をもちますが、キーが違うことに注意してください。 $result と $result_keyed の出力は次のようになります:

Array
(
    [0] => Array
        (
            [0] => green
            [1] => red
        )

    [1] => 4
    [2] => php
)
Array
(
    [2] => Array
        (
            [0] => green
            [1] => red
        )

    [1] => 4
    [0] => php
)

注意: 2 番目のパラメータは、PHP 4.0.3 で追加されました。

array_flip() も参照ください。

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array_reduce

Last updated: Sun, 25 Nov 2007

add a note User Contributed Notes
array_reverse

rdx at jouwmoeder
07-Nov-2006 08:37


As response to Ella's note:



$array[0] = 'record1';

$array[9] = 'record2';

$array[15] = 'record3';



That is ordered way easier AND faster with array_values().

array_reverse twice is unnecessary. Once array_values and all values will be saved in new keys

Ella
14-Jul-2006 09:03


You can also use array_reverse to reset array indexes without losing the order of the values. For example when you use unset() to delete values from an array, the value gets deleted but you end up with a missing index:



$array[0] = 'record1';

$array[9] = 'record2';

$array[15] = 'record3';



Just use:



$array = array_reverse(array_reverse($array));



And your indexes get rearranged:



$array[0] = 'record1';

$array[1] = 'record2';

$array[2] = 'record3';

me2resh at gmail dot com
04-Feb-2005 06:25


Here is my version of sorting multidimensional arrays with any key in it even if u want it alphapatically sorted by any key.



u can remove the strtolower part if you want to keep it case sensitive



function cmp($a, $b){

    return strcmp(strtolower($a["name"]), strtolower($b["name"]));

}

Michiel de Roo
09-Sep-2003 04:55


If you need to reverse an array by reference, you can use the following function.



<?

function &array_reverse_ref(&$a) {

    $r = array();

    for($i=0, $j=count($a); $i<count($a); $i++, $j--) {

        $r[$i] =& $a[$j-1];

    }

    return $r;

}

?>



Use it like: 

<?

class t {

    var $message = "message";    

}

for($i=0; $i<10; $i++) {

    $a[] = new t();

}



$ra =& array_reverse_ref($a);



$a[0]->message = "now... this works in both";

$ra[0]->message = "but.... does not work in both";



for($i=0; $i<10; $i++) {

    echo $ra[$i]->message; echo "<br>\n"; 

}

echo "<br>\n";

for($i=0; $i<10; $i++) {

    echo $a[$i]->message; echo "<br>\n";

}

?>

zee4speed at hotmail dot com
05-Jul-2003 02:56


another way to -> 

If you want to reverse an array with numerical indexes, you can keep them by using following code: 

<?

# this is your array, and you would like to reverse it however maintain their actual index values to point to the existings.

$array_to_reverse[0]="zee";

$array_to_reverse[1]="andrew";

$array_to_reverse[2]="pablo";

$array_to_reverse[3]="mike";

$array_to_reverse[4]="ahmed";

$array_to_reverse[5]="yousra";

$array_to_reverse[6]="samir";

# you want the array to look like this so you can use a command like for each to march through the array.

$array_reversed[6]="samir";

$array_reversed[5]="yousra";

$array_reversed[4]="ahmed";

$array_reversed[3]="mike";

$array_reversed[2]="pablo";

$array_reversed[1]="andrew";

$array_reversed[0]="zee";

# however if you use array_reverse you get this:

$array_reversed[0]="samir";

$array_reversed[1]="yousra";

$array_reversed[2]="ahmed";

$array_reversed[3]="mike";

$array_reversed[4]="pablo";

$array_reversed[5]="andrew";

$array_reversed[6]="zee";

# this causes element samir to be first instead of last, just like you want.  hoever, the index value that refferences samir is now 0 instead of 6

# solution to this is the following code



$array_reversed = array_reverse ($array_to_reverse);

$size_of_array = count($array_reversed);

for ($z = 0; $z < $size_of_array; $z++){

         #do what you want

         #if you want to get the index value of the un-reveresed array, simply

         $actual_index = GetActualIndex($z,$size_of_array);

         echo $z." on array_reversed is the same ".$actual_index." on array_to_reverse<BR>\n";

}



function GetActualIndex($current_index, $size_of_array){

         $reverse_location = abs($current_index + 1 - $size_of_array);

         return $reverse_location;

}

?>

m dot weber at luna-park dot de
01-Feb-2003 12:02


If you want to reverse an array with numerical indexes, you can keep them by using following code:





<?php


end($gruppenarr);


do {


  $part1=key($gruppenarr);


  $part2=current($gruppenarr);


  $gruppenarr2[$part1]=$part2;


} while(prev($gruppenarr));


?>





input is $gruppenarr


output is $gruppenarr2

rahulavhad at yahoo dot com
30-Dec-2000 01:31


This code can help in recursive reversing of the array...





<?php


$arr1 = array(2,1,array(5,2,1,array(9,8,7)),5,0);


$arr1 = array_reverse($arr1);





function Reverse_Array($array)


{    $index = 0;


    foreach ($array as $subarray)


    {    if (is_array($subarray))


        {    $subarray = array_reverse($subarray);


            $arr = Reverse_Array($subarray);


            $array[$index] = $arr;


        }


        else {$array[$index] = $subarray;}


        $index++;


    }


    return $array;


}





$arr2 = Reverse_Array($arr1);


?>

david at audiogalaxy dot com
04-Mar-2000 06:39


As a further clarification: key-value pairs have an order within an array completely separate from whatever the keys happen to be - the order in which you add them.  This is the order that functions like each() and next() will move their pointer through the array.


If you add to an array without specifying the key, like $array[] = value; then an internal counter supplies the key value and then the numerical order of your keys will be identical to the the internal order.  If you "leave holes" - jumping ahead by specifying a higher number for the key, like $array[1000] = value; the internal counter gets pushed forward appropriately.  Other than its effect on this internal counter, specifying a numerical key seems no different than specifying a string. 


However, some array functions, like array_merge() and array_reverse() treat keys that are numbers differently from keys that are not.

david at audiogalaxy dot com
04-Mar-2000 05:40


With associative arrays array_reverse() keeps key => value pairs matched but reverses the order of the array as spaned by functions like each().  With numerical indexes array_reverse not only reverses position (as spaned by each) but also renumbers the keys. 


Both cases seem to be what people would generally want: indeed without the renumbering behavior, someone refering to array elements by numerical key wouldn't think array_reverse did anything.


However, people who are trying to keep numerical keys associated with their values - e.g. trying to have holes in their arrays - will be foiled by the renumbering.  The most telling results come from applying array_reverse() to arrays with mixed keys (some numbers and some strings).  The strings stay attached and the rest of the keys get renumbered around them - most annoying if you are thinking what you've got is an associative array but some of your keys happen to be numbers.

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array_reduce

Last updated: Sun, 25 Nov 2007