PHP - sum values with the same key

Question

What is the best way to sum the 'val' field with the same 'color' for each different color:

Array
(
    [0] => Array
        (
            [color]=> "red"
            [val]=> 4
        )

    [1] => Array
        (
            [color]=> "green"
            [val]=> 3
        )

    [2] => Array
        (
            [color]=> "blue"
            [val]=> 1
        )

    [3] => Array
        (
            [color]=> "green"
            [val]=> 6
        )

    [4] => Array
        (
            [color]=> "blue"
            [val]=> 2
        )
)

Desired result : red: 4; green: 9; blue: 3.

Regards, Elio Fernandes

I'm sure there is a super slick way to do this in one line using array_walk or callbacks, but there is something to be said about the readability of a simple loop. I would loop it. Also, 'best' is subjective. As far as performance is concerned, both methods are probably about the same. — bassxzero
– bassxzero, Commented Nov 7, 2017 at 14:58

GrumpyCrouton · Accepted Answer · 2017-11-07 15:08:05Z

4

I would do it this way, with a foreach loop:

$temp = [];
foreach($arr as $value) {
    //check if color exists in the temp array
    if(!array_key_exists($value['color'], $temp)) {
        //if it does not exist, create it with a value of 0
        $temp[$value['color']] = 0;
    }
    //Add up the values from each color
    $temp[$value['color']] += $value['val'];
}

answered Nov 7, 2017 at 15:08

GrumpyCrouton

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mickaelw · Accepted Answer · 2017-11-07 15:23:50Z

2

You can use array_reduce to have less and more readable code:

$array = array
(
    0 => array("color"=> "red","val"=> 4),
    1 => array("color"=> "blue","val"=> 3),
    2 => array("color"=> "blue","val"=> 1)
);

function sum($accumulator, $item){
    $accumulator[$item['color']] = $accumulator[$item['color']] ?? 0;
    $accumulator[$item['color']] += $item['val'];
    return $accumulator;
}

$sum = array_reduce($array, "sum");
var_dump($sum); // return here array(2) { ["red"]=> int(4) ["blue"]=> int(4) }

And the documentation: http://php.net/manual/en/function.array-reduce.php

edited Nov 7, 2017 at 15:23

answered Nov 7, 2017 at 15:13

mickaelw

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1 Comment

iainn Over a year ago

This doesn't take the colours into account

Josh · Accepted Answer · 2017-11-07 15:06:55Z

1

I would loop it for readability's sake.

$output = array();
foreach($array as $value){
    if(!isset($output[$value['color']])) $output[$value['color']] = 0; //Ensure the value is 0 if it doesn't exist
    $output[$value['color']] += $value['val']; //Add the total for that color
}

This will return an array of colors to total counts.

answered Nov 7, 2017 at 15:06

Josh

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1 Comment

IncredibleHat Over a year ago

I like the simple elegance of just keeping it old school. Clean, direct, to the point.

iainn · Accepted Answer · 2017-11-07 15:18:43Z

1

Personally I'd do something like this with array_reduce, but as mentioned above it might not be the most readable option. Definitely a matter of opinion though.

$result = array_reduce($array, function ($carry, $item) {
    $carry[$item['color']] = $carry[$item['color']] ?? 0;
    $carry[$item['color']] += $item['val'];
    return $carry;
}, []);

See https://eval.in/894644

Edit: Fix notices

edited Nov 7, 2017 at 15:18

answered Nov 7, 2017 at 15:12

iainn

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2 Comments

GrumpyCrouton Over a year ago

Is array_reduce faster than a loop? I like this solution either way, but I'm curious :)

iainn Over a year ago

Can't imagine there's much in it, but if I had to guess I'd say a loop was probably faster. Although obviously unless you're talking about an array with 100,000 items in it, you won't notice.

Krina Mangukiya · Accepted Answer · 2021-08-24 09:13:29Z

To keep up the speed, without the foreach loop, I would say to do it like this:

    $array = [
                [
                    "color" => "red",
                    "val" => "4"
                ],
                [
                    "color" => "green",
                    "val" => "3"
                ],
                [
                    "color" => "blue",
                    "val" => "1"
                ],
                [
                    "color" => "green",
                    "val" => "6"
                ],
                [
                    "color" => "blue",
                    "val" => "2"
                ]
       ];

    $array = array_values(array_reduce(
         $array,

           function (array $a, array $v) {
              $k = "".$v['color']."";
                    
              if (!array_key_exists($k, $a)) {
                  $a[$k] = $v;   
              } else {
                  $a[$k]['val'] += $v['val'];
              }
              return $a;              
          },
       array()                   
    ));

var_dump($array);

Alaa Aqeel · Accepted Answer · 2017-11-07 15:25:35Z

-1

$arrays = array( 
         array(
                "color"=>"red",
                "val"=>4
         ),
         array( 
               "color"=>"green",
               "val"=>3
        )
);
foreach ($color as $array) {
    echo $array["color"].": ".$array["val"].";";
}

edited Nov 7, 2017 at 15:25

answered Nov 7, 2017 at 15:20

Alaa Aqeel

6558 silver badges18 bronze badges

1 Comment

IncredibleHat Over a year ago

This will spew notices all over.

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