How to get all values of one key from laravel multidimensional array

Question

I have a multidimensional Laravel collection of pages for a navigation menu.

{
    id: 1,
    ...
    children: [
        {
            id: 2,
            ...
            children: [
                {
                    id: 3,
                    ...
                    children: []
                }
            ]
        },
        {
             id: 4,
             ...
             children: []
        }
    ]
}

The collection has no limit on its depth or the amount of siblings for each tier. However, there is only one page at the root level. i.e. the first page (id 1) has no siblings. How can I extract all the ids into a single array?

expected output

[1,2,3,4]

Have you tried pluck('children.id')? Not sure if pluck() supports dot syntax. — miken32
– miken32, Commented Jan 26, 2021 at 23:53
Pluck only returns the first level id. children.pluck returns null — BobbyP
– BobbyP, Commented Jan 27, 2021 at 0:00
array_column seems to get the values from an array of arrays. This structure is many levels deep, and so this isn't working — BobbyP
– BobbyP, Commented Jan 27, 2021 at 0:30

IGP · Accepted Answer · 2021-01-27 01:13:46Z

I got the result you want with the following test object.

$object = [
    (object)['id' => 1, 'children' => []],
    (object)['id' => 2, 'children' => [
        (object)['id' => 4, 'children' => [
            (object)['id' => 6, 'children' => []]
        ],
        (object)['id' => 5, 'children' => []]
    ],
    (object)['id' => 3, 'children' => []]
]

=> [
     {#4565
       +"id": 1,
       +"children": [],
     },
     {#4605
       +"id": 2,
       +"children": [
         {#4567
           +"id": 4,
           +"children": [
             {#4563
               +"id": 6,
               +"children": [],
             },
           ],
         },
         {#4564
           +"id": 5,
           +"children": [],
         },
       ],
     },
     {#4551
       +"id": 3,
       +"children": [],
     },
   ]

To manage it, I had to use some recursion. I am not sure it's the best but it gets the job done.

function getIds($item) {
    return [$item->id, collect($item->children)->map('getIds')->all()];
}

$ids = collect($object)
    ->map('getIds')  // call getIds function which will in turn do the same for all children
    ->flatten()      // flatten the resulting array
    ->sort()         // sort the resulting ids since they probably won't be in order
    ->values()       // only interested in the values, not the keys
    ->all();         // transform collection to array

EDIT: Found a way to further inlne this.

$ids = collect($object)
    ->map($closure = function($item) use (&$closure) {
        return [$item->id, collect($item->children)->map($closure)->all()];
    })
    ->flatten()
    ->sort()
    ->values()
    ->all();

I don't understand it. But it works perfectly. Thanks for your help

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