PHP sum array values by item.qty - php

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.