How can I paginate a merged collection in Laravel 5?

If you want to use a LengthAwarePaginator simply instantiate one. As mentioned in the comments of a previous answer you will have to set the path for this. You will also need to make sure you resolve the "currentPage" and set the items to be returned before you instantiate the paginator. This can all be done before/on instantiation. So a function may look something like:

function paginateCollection($collection, $perPage, $pageName = 'page', $fragment = null)
{
    $currentPage = \Illuminate\Pagination\LengthAwarePaginator::resolveCurrentPage($pageName);
    $currentPageItems = $collection->slice(($currentPage - 1) * $perPage, $perPage);
    parse_str(request()->getQueryString(), $query);
    unset($query[$pageName]);
    $paginator = new \Illuminate\Pagination\LengthAwarePaginator(
        $currentPageItems,
        $collection->count(),
        $perPage,
        $currentPage,
        [
            'pageName' => $pageName,
            'path' => \Illuminate\Pagination\LengthAwarePaginator::resolveCurrentPath(),
            'query' => $query,
            'fragment' => $fragment
        ]
    );

    return $paginator;
}

use Illuminate\Pagination\LengthAwarePaginator;
use Illuminate\Support\Collection;
use Illuminate\Pagination\Paginator;

You can add the following code for Collection in the Providers/AppServiceProvider inside public function boot() .

    // Enable pagination
    if (!Collection::hasMacro('paginate')) {

        Collection::macro('paginate', 
            function ($perPage = 15, $page = null, $options = []) {
            $page = $page ?: (Paginator::resolveCurrentPage() ?: 1);
            return (new LengthAwarePaginator(
                $this->forPage($page, $perPage)->values()->all(), $this->count(), $perPage, $page, $options))
                ->withPath('');
        });
    }

Then, you can call paginate from a Collection, just like an Eloquent model. For example

$pages = collect([1, 2, 3, 4, 5, 6, 7, 8, 9])->paginate(5);

however paginate is for eloquent models and DB queries, and not collections, it seems.

You are right. but there is ineed a paginator function for collections. forPage

Syntax:

Collection forPage(int $page, int $perPage)

Example:

Rest is simple.

public function foo()
{
    $collection = collect([1,2,3,4,5,6,7,8,9,0]);
    $items = $collection->forPage($_GET['page'], 5); //Filter the page var
    dd($items);
}