array_reduce

说明

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

array_reduce() 将回调函数 function 迭代地作用到 input 数组中的每一个单元中，从而将数组简化为单一的值。如果指定了可选参数 initial，该参数将被当成是数组中的第一个值来处理，或者如果数组为空的话就作为最终返回值。如果数组为空并且没有传递 initial 参数，array_reduce() 返回 NULL。

例 1. array_reduce() 例子


<?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);
?>

这将使 $b 的值为 15，$c 的值为 1200（= 10*1*2*3*4*5），以及 $d 的值为 1。

参见 array_filter()，array_map()，array_unique() 和 array_count_values()。

add a note User Contributed Notes

Janez R.
30-Jul-2007 03:27


--REPOST, fixed some typos, please replace previous note--

In PHP ver. 4.3.1 the initial value parameter allowed for string type also. In PHP ver. 5.1.6 this param is now converted to int and callback function will receive number 0 when initial param is an empty string.



<?php

function arc ($reduced, $item)

{

  $reduced = $item.$reduced;

  return $reduced;

}



array_reduce( array(a,b,c), "arc", "" );

?>



Output in PHP 4.3.1: cba

Output in PHP 5.1.6: cba0



Possible solution:

<?php

function arc ($reduced, $item)

{

  if ($reduced === 0)  $reduced = "";

  $reduced = $item.$reduced;

  return $reduced;

}

?>

Janez R.
30-Jul-2007 03:05


In PHP ver. 4.3.1 the initial value parameter allowed for string type also. In PHP ver. 5.1.6 this param is now converted to int and callback function will receive number 0 when initial param his an empty string.



<?php

function arc ($reduced, $item)

{

  $reduced = $item.$reduced;

  return $reduced;

}



arc( array(a,b,c), "arc", "" );

?>



Output in PHP 4.3.1: cba

Output in PHP 5.1.6: cba0



Possible solution:

<?php

function arc ($reduced, $item)

{

  if ($reduced === 0)  $reduced = "";

  $reduced = $item.$reduced;

  return $reduced;

}

?>

yuki [dot] kodama [at] gmail [dot] com
31-Jan-2007 04:56


This code will reduce array deeply.



<?php

function print_s($s) {

    return is_null($s) ? "NULL" : (is_array($s) ? "Array" : ($s ? "TRUE" : "FALSE"));

}

function r_and_dp($a, $b) {

    echo "phase1:" . print_s($a) . "," . print_s($b) . "<br>\n";

    if(is_array($a)) {

        $a = array_reduce($a, "r_and_dp");

    }

    if(is_array($b)) {

        $b = array_reduce($b, "r_and_dp");

    }

    echo "phase2:" . print_s($a) . "," . print_s($b) . "<br>\n";

    $a = is_null($a) ? TRUE : $a;

    $b = is_null($b) ? TRUE : $b;

    echo "phase3:" . print_s($a) . "," . print_s($b) . "<br>\n";

    return $a && $b;

}

$bools = array(TRUE, array(FALSE, TRUE), TRUE);

echo print_s(array_reduce($bools, "r_and_dp")) . "<br>\n";



// result: FALSE

?>



When using boolean, you have to carefully set an "initial" argument.



<?php

function r_or_dp($a, $b) {

    if(is_array($a)) {

        $a = array_reduce($a, "r_or_dp");

    }

    if(is_array($b)) {

        $b = array_reduce($b, "r_or_dp");

    }

    return (is_null($a) ? FALSE : $a) || (is_null($b) ? FALSE : $b);

}

?>

bdechka at yahoo dot ca
10-Jan-2007 08:57


The above code works better this way.



<?php

function reduceToTable($html, $p) {

   $html .= "<TR><TD><a href=\"$p.html\">$p</a></td></tr>\n";

   return $html;

}



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



$tab = array_reduce($list, "reduceToTable");

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

?>

marcel dot oehler at kubusmedia dot com
08-Feb-2006 03:26


I've just experienced some really strange behaviour of array_reduce in PHP 5.0.4:



$result = array( 0, 17, 0, 0, 33, 0, 0, 0, 0, 50);

$total = array_reduce( $result, "sumCalc", 0);



function sumCalc( $a, $b){

    return $a + $b;

}



and $total equals to 83!



I know, this could be done easier, but it should work nevertheless. Has anybody experienced something similar? I will avoid using array_reduce in the future...

Seanj.jcink.com
05-Jan-2006 02:23


The code posted below by bishop to count the characters of an array is simply... erm... well useless to me...



$array=Array("abc","de","f");

strlen(implode("",$array)); //6



works; and is much smaller. Probably much faster too.

ildar [DASH] sh [AT] mail [DOT] ru
30-Nov-2005 06:02


in rare cases when an array is a set of numeric values and result is one of sum or product of numbers the next examples may be useful



<?php



// sum of array items

echo eval('return ' . implode('+', $nums) . ';');



// product of array items

echo eval('return ' . implode('*', $nums) . ';');



?>



the reason of these codes is omitting of single used per script of callbacks

david dot tulloh at infaze dot com dot au
23-Jun-2005 08:18


The code supplied by cuntbubble is unfortunately incorrect.



Running it I got the output:

0<TR><TD><a href="page1.html">page1</a></td>

<TR><TD><a href="page2.html">page2</a></td>

<TR><TD><a href="page3.html">page3</a></td>

</table>



So php, not finding an integer, used int(0) to start the process.  I've tested to confirm this.

bishop
01-May-2004 03:19


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 03:17


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 04:08


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) {


    $html .= "<TR><TD><a href=\"$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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