[5.1] Add split method into collection

[arrilot]

Use case:
I need to split a collection of arbitary length into 3 columns of relatively equal length.

Notes:

1. Maybe divide is a better name?
2. Should we care about preserving the keys? In this implementation they never preserve.

[arrilot]

ping @JosephSilber

[JosephSilber]

How is this different than the existing chunk method?

[arrilot]

This splits the collection into N pieces.
Chunk breaks the collection into collections with N items each

[GrahamCampbell]

cs

[JosephSilber]

So it's the same as this?

$users->chunk(ceil($users->count() / $n));

...and this even preserves the keys.

[arrilot]

There is a small difference - there are always exactly N pieces in the result collection
collect([1,2])->chunk(ceil($users->count() / 3))->toArray();
gives

[
   [1],
   [2],
]

collect([1,2])->split(3)->toArray();
gives

[
   [1],
   [2],
   [],
]

It's way more simple and clear too

[JosephSilber]

forPage calls slice, which calls array_slice with the $preserve_keys flag set to true.

Why doesn't it preserve the keys?

[arrilot]

Huh? https://github.com/laravel/framework/blob/5.1/src/Illuminate/Support/Collection.php#L530

[JosephSilber]

That's been changed in 5.2.

The slice method now preserves keys, not even giving you the choice to override it.

We're moving away from all these Boolean flags. Wherever possible, keys should be preserved. If you don't want that, call values on the result (recursively if needed).

[arrilot]

Oh, as well as chunk I see

So it doesn't preserve in 5.1 but gonna preserve in 5.2...

Maybe this PR should go to master then or be changed to preserve in 5.1 too? Let's leave it up to Taylor to decide

[taylorotwell]

Going to hold off on this.