Finding average number from array using array_reduce

Question

I have an array that consists of names of people and their height. I need to find the average height using the function array_reduce which is wrapped in a function assigned to a variable. Below is the code I wrote so far. Everything seems to be working until I pass the array to the array_reduce function which is then NULLed. I tried to explain it with comments in the code. Why is the array suddenly deleted and how do I pass it to the most inner function?

$people = [
  ['name'=> 'John'  , 'height'=> 1.65],
  ['name'=> 'Peter' , 'height'=> 1.85],
  ['name'=> 'Silvia', 'height'=> 1.69],
  ['name'=> 'Martin', 'height'=> 1.82]
];


$filter = function  ($people)
{
    $averageHeight = 0;
    $count = count($people);
    echo $count;
    //if I var_dump($people) - the array $people is FINE.
    return array_reduce(
            $people,
            function ($people) use (&$averageHeight, &$count)
            {
                $averageHeight += $people['height'] / $count;    
                return $averageHeight;
                //var_dump($people); - var people is NULL. Where did it go?
            }
    );
};

print_r($filter($people));

The reason $people is null is because it's the first function parameter you named people and not the actual array you declared above. PHP refers to this parameter as $carry which is the carried value. If you don't provide a default carry value it starts off as null. — apokryfos
– apokryfos, Commented Sep 27, 2017 at 13:36
And an alternative way of calculating the average height: $averageHeight = array_sum(array_column($people, 'height')) / count($people); — Mark Baker
– Mark Baker, Commented Sep 27, 2017 at 13:42

apokryfos · Accepted Answer · 2017-09-27 13:57:15Z

3

This is how you can use array_reduce to get an average:

function array_average($array) {
    $carry = null;
    $count = count($array);
    return array_reduce($array, function ($carried, $value) use ($count) {
         return ($carried===null?0:$carried) + $value/$count;
    },$carry);
}

The function will take the accumulator and the value as parameters and should return the value to be carried to the next element.

You can use it as:

 $averageheight = array_average(array_column($people,"height"));

This results in:

1.7525

Here's an example:

http://sandbox.onlinephpfunctions.com/code/a0bd15fb66061340ceca9e743418575d7990b6c3

If you need this whole thing as a callable then do:

function array_average($array) {
    $carry = null;
    $count = count($array);
    return array_reduce($array, function ($carried, $value) use ($count) {
         return ($carried===null?0:$carried) + $value/$count;
    },$carry);
}

$filter = function ($people) {
     return array_average(array_column($people,"height"));
};

 print_r($filter($people));

http://sandbox.onlinephpfunctions.com/code/dd2ec178be3989f8d9dd9d9ef5d270c7d40b8be7

edited Sep 27, 2017 at 13:57

answered Sep 27, 2017 at 13:32

apokryfos

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2 Comments

pidari Over a year ago

Okay, this works and is great but I need to assign the function to a variable. I tried like this print_r($filter(array_average(array_column($people,"height")))); but I get Parse error: syntax error, unexpected 'print_r' (T_STRING)

apokryfos Over a year ago

@pidari updated. You can also declare the function inside the variable but it's quite a generic one so you may find uses for it elsewhere as well.

Kmg Kumar · Accepted Answer · 2017-09-27 14:00:26Z

0

Use this code, where the total array count we didn't find out inside the sum function so, i will use this into the print_r() function.


<?php

function sum($carry, $p)
{
    $carry += $p['height'];
    return $carry;
}

$people = [
  ['name'=> 'John'  , 'height'=> 1.65],
  ['name'=> 'Peter' , 'height'=> 1.85],
  ['name'=> 'Silvia', 'height'=> 1.69],
  ['name'=> 'Martin', 'height'=> 1.82]
];

$k = 0;
$k = array_reduce($people ,"sum");
print_r($k/count($people));
?>

answered Sep 27, 2017 at 14:00

Kmg Kumar

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