[Proposal] Diffing of Eloquent collections

[dwightwatson]

i would like to propose the inclusion of diffing of Eloquent collections. This feature could be useful in belongsToMany relationships, for example if a blog Post belonged to many Categories, you could find the categories it doesn't belong to by diffing the collections.

My proposed implementation is below and I have a branch ready with tests to make a pull request if this is accepted.

public function diff(Collection $collection)
{
    $diff = new static;

    foreach ($this->items as $item)
    {
        if ( ! $collection->contains($item->getKey()))
        {
            $diff->add($item);
        }
    }

    return $diff;
}

[ipalaus]

Oh!! Nice idea, I would love to have that feature.

[Anahkiasen]

Wouldn't the following work ?

$diff = array_diff($this->items, $collection->all());

return new static($diff);

[JoostK]

@Anahkiasen That requires identical objects, the proposed code checks for id's. Would probably both work when results are directly from the DB, but will be different when there's a slight difference between the objects.

[lucasmichot]

I think these 3 methods could be very useful:

// $this contains X and Y, $collection contains Y and Z => returns X
public function diff(Collection $collection, $check_id = true) {...}

// $this contains X and Y, $collection contains Y and Z => returns X, Y, Z
public function merge(Collection $collection, $check_id = true) {...}

// $this contains X and Y, $collection contains Y and Z => returns Y
public function intersect(Collection $collection, $check_id = true) {...}

If check_id is true, comparison can be done against ids ( @dwightwatson 's approach ); if false comparison will be done against the collection item ( @Anahkiasen 's approach ).

[dwightwatson]

I've implemented mergeCollection, diffCollection and intersectCollection methods using the getKey() approach with tests here: dwightwatson@0c9a4f7.

[lucasmichot]

Great @dwightwatson , you should make a Pull Request !

[taylorotwell]

Feel free to make pull requests.