PHP - Loop through array and print out value only if it changes between iteration

Question

Apologies if this has been asked but I can't find a solution that meets my needs.

I have an array in a PHP 7 application as follows:

$data = [
    0 => [
        'regulations_label' => 'Europe',
        'groups_label' => 'G1',
        'filters_label' => 'FF1'
    ],
    1 => [
        'regulations_label' => 'Europe',
        'groups_label' => 'G1',
        'filters_label' => 'FF900'
    ],
    2 => [
        'regulations_label' => 'Europe',
        'groups_label' => 'G1',
        'filters_label' => 'FF324234'
    ],
    3 => [
        'regulations_label' => 'Europe',
        'groups_label' => 'G2',
        'filters_label' => 'FF23942'
    ],
    4 => [
        'regulations_label' => 'America',
        'groups_label' => 'G29',
        'filters_label' => 'FF3242'
    ],
    5 => [
        'regulations_label' => 'America',
        'groups_label' => 'G29',
        'filters_label' => 'FF78978'
    ],
    6 => [
        'regulations_label' => 'America',
        'groups_label' => 'G29',
        'filters_label' => 'FF48395043'
    ],
    7 => [
        'regulations_label' => 'Asia',
        'groups_label' => 'G2000',
        'filters_label' => 'FF7'
    ],
    // ...
];

The output I want to achieve is like this:

Europe
    - G1
        -- FF1
        -- FF900
    - G2
        -- FF23942

America
    - G29
        -- FF3242
        -- FF48395043

Asia
    - G2000
        -- FF7

Essentially all it's doing is outputting the array in a structured format such that it shows the regulations_label followed by any corresponding groups_label and then any filters_label.

It's simple enough to loop through the entire array, e.g.

foreach ($data as $d) {
    echo $d['regulations_label'] . "\n";
    echo ' - ' . $d['groups_label'] . "\n";
    echo ' -- ' . $d['filters_label'] . "\n";
}

However this introduces "duplicate" headings for regulations_label and groups_label because it's printing every single key. But I don't see how I can check if this has changed during the foreach statement because $d is always the current element.

I was attempting to do a check based on the previous array key:

foreach ($data as $key => $d) {
   if ($data[$key-1]['regulations_label'] !== $d['regulations_label']) {
       echo $d['regulations_label'] . "\n";
       echo "-" . $d['groups_label'] . "\n";
   }
}

The trouble is that this then just prints 1 groups_label so I'd end up with - for example:

Europe
- G1
America
...

It wouldn't get as far as "G2".

I can't help but think I'm going about this in a bizarre way. Can anyone advise a better solution?

Background info: The data I receive in $data isn't something I can modify because that format is required for the use case which is a feature in an application like this: jQuery load more data on scroll

Answer 1

you can use foreach and group by using regulations_label and groups_label

$group = [];
foreach($data as $v){
  $group[$v['regulations_label']][$v['groups_label']][] = $v['filters_label'];
}

DEMO