PHP sum array values by item.qty

Question

I wonder if there is a faster way to sum i.e. the weight of each item by qty.

$items = [
    [
        'qty'    => 1,
        'weight' => 1,
    ],
    [
        'qty'    => 2,
        'weight' => 1,
    ],
    [
        'qty'    => 3,
        'weight' => 1,
    ],
];

$totalWeight = 0.0;
foreach ($items as $item) {
    $totalWeight += $item['weight'] * $item['qty'];
}
echo $totalWeight . PHP_EOL;

If i would not need the qty offset, i just could use

array_sum(array_column($items, 'weight'))

But this wont work ofc in this example.

Anybody has an idea if and how this could be done faster?

Thanks /cottton

EDIT

Test script:

$items = [];
for ($i = 0; $i < 1000; $i++) {
    $items[] = [
        'foo'    => 1,
        'qty'    => $i,
        'bar'    => 2,
        'weight' => $i,
        'baz'    => 3,
    ];
}
$totalWeight = 0.0;


$start = microtime(true);
for ($i = 0; $i < 10000; $i++) {
    $totalWeight = 0.0;
    foreach ($items as $item) {
        $totalWeight += $item['weight'] * $item['qty'];
    }
}
$elapsed = sprintf('%f', microtime(true) - $start);
echo "Elapsed: {$elapsed}\r\n";
echo "Total weight: {$totalWeight}\r\n";
// Elapsed: 0.744311
// Total weight: 332833500

Answer 1

Use https://www.w3schools.com/php/func_array_reduce.asp

    <?php
    $items = [
        [
            'qty'    => 1,
            'weight' => 1,
        ],
        [
            'qty'    => 2,
            'weight' => 1,
        ],
        [
            'qty'    => 3,
            'weight' => 1,
        ],
    ];


    $totalWeight = array_reduce($items, 
        function($acc, $e) { return $acc + ($e['weight'] * $e['qty']); });
    echo $totalWeight . PHP_EOL;

?>

Answer 2

You can map array_product over the inner arrays and array_sum the resulting array of products.

$totalWeight = array_sum(array_map('array_product', $items));

(This may not work if the example you showed was simplified for the the question here and the inner arrays include other fields that aren't shown.)

Answer 3

Here is a method that loops the unique weights and finds the sum of qty of each weights and multiply it with the weight.

In your case it makes one loop.

$weights = array_column($items, 'weight');
$result =0;
Foreach(array_unique($weights) as $weight){
    // Finds the items with the weight 1 for example
    $weightitems = preg_grep("/". $weight . "/", $weights);
    // Sum quantity of items with the weight of 1 and multiply with weight (1).
    $result += array_sum(array_column(array_intersect_key($items, $weightitems), "qty")) * $weight;
}
Echo $result;

Notice I added a "5" just to see that it worked correct in my example code.

https://3v4l.org/V293P

---

A slightly more optimized code, but still not faster than a simple loop as far as I can see.
I can make it 4-ish times slower depending on the input but I can't get it closer than that.

$weights =array_unique(array_column($items, 'weight'));
$result =[];
Foreach($weights as $weight){
    $weightitems = array_filter($items, function ($var) use ($weight) {
        return ($var['weight'] == $weight);
    });
    $result[] = array_sum(array_column($weightitems, "qty")) * $weight;
}
Echo array_sum($result) ."\n";

https://3v4l.org/aB7d9

---

How accurate does it have to be?

This is faster than looping but is off by 1 on 3000 items and a total of 17992.
Is that within error margin, then this is faster.

I calculate the average of the sumproduct of the two columns using array_sum, array_column and count.

$count = count($items);
$weights = array_sum(array_column($items, 'weight'));
$qty = array_sum(array_column($items, 'qty'));

Echo ($qty * $weights)/$count ."\n";
// 17991 (should be 17992)

https://3v4l.org/c3CIg

I think I have tried all possible solutions now.