Multiplying array indexes in PHP with array_reduce

Question

Why does the array_reduce() method work differently when adding and multiplying? When I add the array values below, the code produces the expected result: 15. But when I multiply, it returns: 0. Same code... The only difference is that the + sign is switched for the * sign.

  function sum($arr){
        print_r(array_reduce($arr, function($a, $b){return $a + $b;}));
    }

    function multiply($arr){
        print_r(array_reduce($arr, function($a, $b){return $a * $b;}));
    }

    sum(array(1, 2, 3, 4, 5)); // 15
    multiply(array(1, 2, 3, 4, 5)); // 0

Hakem · Accepted Answer · 2015-06-01 05:02:34Z

5

According to documentation, you might wanna try

function multiply($arr){
        print_r(array_reduce($arr, function($a, $b){return $a * $b;},1));
}

Here is a quote from this discussion:

The first parameter to the callback is an accumulator where the result-in-progress is effectively assembled. If you supply an $initial value the accumulator starts out with that value, otherwise it starts out null.

edited Jun 1, 2015 at 5:02

answered Jun 1, 2015 at 4:45

Hakem

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4 Comments

Tomaso Albinoni Over a year ago

Beat me to it by 20 seconds

Tomaso Albinoni Over a year ago

Here's a link to the documentation: php.net/manual/en/function.array-reduce.php

Hakem Over a year ago

@shmuli becausee you need to set an initial value, it seems $a in the first round is 0 so everything is multiplied by 0

someOne Over a year ago

@shmuli this is the elaborate discussion about the "why", and Hakem, you may provide an appropriate quote of that note in your answer, for the future visitors.

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