reducing an array into another array - php

Question

Inside a laravel blade template, I am trying to reduce an array like this:
$longList = [['box' => 1, 'kg' => 2], ['box' => 2, 'kg' => 2], ['box' => 3, 'kg' => 3]];
into something like this:
$reducedList = [['count' => 2, 'kg' => 2], ['count' => 1, 'kg' => 3]];
This is what I have so far:
#php
$variableWeights = isset($sale->variable_weight_json) ? collect(json_decode($sale->variable_weight_json, true)) : null;
$groups = array();
if (isset($variableWeights)) {
$groups = $variableWeights->reduce(function($carry, $item) {
$index = array_search($item['kg'], array_column($carry, 'weight'));
if (isset($index)) {
$existing = $carry[$index];
array_splice($carry, $index, 1, [
'count' => $existing['count'] + 1,
'weight' => $item['kg']
]);
} else {
array_push($carry, [
'count' => 1,
'weight' => $item['kg'],
]);
}
return $carry;
}, array());
}
#endphp
But it is giving me the error Undefined offset: 0
I am new to php. How should the code be corrected or is there a better approach to achieve the desired result?

Answer 1

Why dont you reduce it to something simpler like this
$reducedList = [2 => 2, 3 => 1]
where the weight is the index and the value is the count.
$reducedList = [];
foreach ($longList as $box) {
if (isset($reducedList[$box['kg']]) {
$reducedList[$box['kg']]++;
} else {
$reducedList[$box['kg']] = 1;
}
}
This way you avoid complexity but you still get the same amount of information.

Answer 2

I guess you can achieve it with code like:
$longList = [['box' => 1, 'kg' => 2], ['box' => 2, 'kg' => 2], ['box' => 3, 'kg' => 3]];
$reducedList = array_values(array_reduce(
$longList,
function($carry, $item) {
if (isset($carry[$item['kg']])) {
++$carry[$item['kg']]['count'];
} else {
$carry[$item['kg']] = ['count' => 1, 'kg' => $item['kg']];
}
return $carry;
},
[]
));
print_r($reducedList);
Here is a working example.

Answer 3

don't use isset() function. it checks only variable existing. use empty() or other condition, it will check variable existing and value. try this.
#php
$variableWeights = isset($sale->variable_weight_json) ? collect(json_decode($sale->variable_weight_json, true)) : null;
$groups = array();
if ($variableWeights->isNotEmpty()) {
$groups = $variableWeights->reduce(function($carry, $item) {
$index = array_search($item['kg'], array_column($carry, 'weight'));
if ($index != false ) {
$existing = $carry[$index]?: false;
if ($existing) {
array_splice($carry, $index, 1, [
'count' => $existing['count'] + 1,
'weight' => $item['kg']
]);
}
} else {
array_push($carry, [
'count' => 1,
'weight' => $item['kg'],
]);
}
return $carry;
}, array());
}
#endphp

Answer 4

You can use the sexy countBy() method (combined with the famous map() one) of the Collection class.
Try this:
$longList = [['box' => 1, 'kg' => 2], ['box' => 2, 'kg' => 2], ['box' => 3, 'kg' => 3]];
$shortList = collect($longList)
->countBy('kg')
->map(function ($count, $kg) {
return [
'kg' => $kg,
'count' => $count,
];
});
With that, you'll get this:
dd($shortList);
=> Illuminate\Support\Collection {#3380
all: [
2 => [
"kg" => 2,
"count" => 2,
],
3 => [
"kg" => 3,
"count" => 1,
],
],
}
Here you have a working demo.

Answer 5

isset checks if variable is set (i.e it exists and not NULL). As I (and core developers) can hardly imagine in which cases array_search can return NULL, there's a manual which says:
Returns the key for needle if it is found in the array, FALSE otherwise.
So, you need to check if $index is not false:
$index = array_search($item['kg'], array_column($carry, 'weight'));
// Note that I use `!==` because using `!=` will convert
// `0` index to false, which is not correct in your case
if (false !== $index) {