PHP: array_reduce

説明

mixed array_reduce ( array input, callback function [, int initial])

array_reduce()は、配列input の各要素にfunction関数を繰り返し適用し、配列を一つの値に減らします。オプションintial が利用可能な場合、処理の最初で使用されたり、配列が空の場合の最終結果として使用されます。

例 1. array_reduce()の例

<?php function rsum($v, $w) { $v += $w; return $v; } function rmul($v, $w) { $v *= $w; return $v; } $a = array(1, 2, 3, 4, 5); $x = array(); $b = array_reduce($a, "rsum"); $c = array_reduce($a, "rmul", 10); $d = array_reduce($x, "rsum", 1); ?>

これにより、$bの値は15 となり、$cの値は 1200 (= 1*2*3*4*5*10)、そして、 $dの値は1となります。

array_filter(), array_map()も参照下さい。

add a note User Contributed Notes
array_reduce

bishop
01-May-2004 05:19


Count the total number of characters in an array of strings:



<?php

$lines = array ('abc', 'd', 'ef');

$totalChars = array_reduce($lines, create_function('$v,$w','return $v + strlen($w);'), 0);

// $totalChars === 6

?>

tonicpeddler at aol dot com
02-Nov-2002 04:17


in response to php dot net at cuntbubble dot com



actually when you pass a value to a function that accepts a specific data type, php automatically evaluates that value as the data type expected

php dot net at cuntbubble dot com
18-Jan-2002 05:08


There is an error/misleading item in the documentation





[, int initial]





int is not constrained to an integer, it can be any data type (although I've not tested ALL data types)





and $v is the cumulative part, the current value of the reduction.





and I'll take the liberty to add another example, as used in my code





<?php


function reduceToTable($html, $p) {


    $html .= "<TR><TD><a href=/old?u=http%3A%2F%2Ffr.php.net%2Fmanual%2Fja%2F%5C&y=1999"$p.html\">$p</a></td>\n";


    return $html;


}





$list = Array("page1", "page2", "page3");





$tab = array_reduce($list, "reduceToTable", "<table>\n");


echo $tab . "</table>\n";


?>





hmm, getting stuff on one line sure is tricky, it get's wordwrapped on the char count in html so &gt; counts as 4 chars not one so by the time you've counted "< you've used up 8 chars


If it get's through moderation could someone please make it look ok :)

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