reducing an array into another array

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?

N69S · Accepted Answer · 2020-03-05 15:42:27Z

2

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.

answered Mar 5, 2020 at 15:42

N69S

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Comments

Andrii Filenko · Accepted Answer · 2020-03-05 15:44:28Z

1

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.

answered Mar 5, 2020 at 15:44

Andrii Filenko

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Comments

Shahadat Hossain · Accepted Answer · 2020-03-05 15:47:52Z

1

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

edited Mar 5, 2020 at 15:47

answered Mar 5, 2020 at 15:35

Shahadat Hossain

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1 Comment

N69S Over a year ago

$index can have the value 0 and be valid. isset() or empty wont change much.

Kenny Horna · Accepted Answer · 2020-03-05 16:15:26Z

1

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.

edited Mar 5, 2020 at 16:15

answered Mar 5, 2020 at 15:49

Kenny Horna

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Comments

u_mulder · Accepted Answer · 2020-03-05 15:44:32Z

0

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) {

answered Mar 5, 2020 at 15:44

u_mulder

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