Laravel 5 Collections: Reducing a Multi-Dimensional Collection to a Single Dimension Losing Keys With flatten

The flatten method will return a new Collection instance representing a flattened version of the original collection's items. The flatten method internally makes use of the "Illuminate\Support\Arr::flatten($array)" helper method. The flatten method will not preserve any keys from the original collection.

#Signature

1public function flatten(
2    $depth = INF
3);

#Example Use

The following example demonstrates the usage of the flatten method:

 1use Illuminate\Support\Collection;
 2 
 3// Create a new collection instance.
 4$collection = new Collection([
 5    'first',
 6    'second' => [
 7        'nested',
 8        'array',
 9        [
10            'deeply',
11            'nested'
12        ]
13    ],
14    'third' => 'some-value'
15]);
16 
17// Flatten the original collection.
18$flattenedCollection = $collection->flatten();

The $flattenedCollection variable will hold an instance of the Collection class and will have a value similar to the following output:

1object(Illuminate\Support\Collection)
2  protected 'items' =>
3    array
4      0 => string 'first'
5      1 => string 'nested'
6      2 => string 'array'
7      3 => string 'deeply'
8      4 => string 'nested'
9      5 => string 'some-value'

It is obvious in the above output that the flatten method does not preserve any of the original keys, and will even flatten deeply nested arrays.

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