A join collection macro

join.php

<?php

Collection::macro('join', function ($items, callable $callback) {
    return $this->flatMap(function ($value) use ($items, $callback) {
    	return $items->filter(function ($item) use ($value, $callback) {
        	return $callback($value, $item);
        })->map(function ($item) use ($value) {
        	return new Collection([$value, $item]);
        });
    });
});

$first = collect([0, 1, 2]);
$second = collect([0, 0, 1]);

$result = $first->join($second, function ($a, $b) {
    return $a == $b;
});

dd($result);