[5.4] Create a mapToGroups method

[JosephSilber]

$users->mapToGroups(function ($user) {
    return [$user->country => $user->id];
});

/*
    [
        'canada' => [23, 1],
        'france' => [34, 3],
        'germany' => [9],
        'us' => [4, 7, 2],
    ]
*/

[thecrypticace]

Seems neat. I have, on occasion, needed to use ->map after a groupBy so this could be a neat addition. I'm not 100% on the name mapToGroups though. Doesn't feel right but I can't think of a better one.

Also, the above example with Higher Order Messages can be written as:

$users->groupBy("country")->map->pluck("id");

Want to see something even crazier? Add a groupBy proxy and you can write it like this:
Warning: Please don't actually do this. Code readability and intent are important

$users->groupBy->country->map->map->map->id;

Aside: keyBy and groupBy both would benefit from being in the default proxy list. Not sure why they weren't included. I know you can add them with Collection::proxy but it still seems like a sensible default.

[JosephSilber]

the above example with Higher Order Messages can be written as

I intentionally created a simple example. But if you do more complex stuff, you may end up with two closures.

Additionally, if the value you're mapping to requires the original key, you're out of luck without this mapToGroups. You'd have to resort back to an ugly foreach.

[thecrypticace]

I intentionally created a simple example. But if you do more complex stuff, you may end up with two closures.

Yeah, I figured as much. Was just pointing it out.

you're out of luck without this mapToGroups

Yeah. What I usually try to do is map first and include an extra entry for grouping if needed. But I always felt that it was a bit of a hack. Just depends on use case.

[ConnorVG]

I feel like this should follow the naming of flatMap and be named groupMap.

[JosephSilber]

@ConnorVG to me, groupMap would mean something else. I'd expect groupMap to work like this:

$collection = collect([
    'a' => [2, 5],
    'b' => [8, 9],
]);

$collection->groupMap(function ($number) {
    return $number * 2;
});

/*
    [
        'a' => [4, 10],
        'b' => [16, 18],
    ]
*/

...which would also maybe be a useful method, but this mapToGroups does something else.

[ConnorVG]

Eh? That's just a map map.

[fernandobandeira]

I think we could add another test for numeric keys:

$users->mapToGroups(function ($user) {
    return [$user->age => $user->id];
});

/*
    [
        17 => [23, 1],
        23 => [34, 3],
        31 => [9],
        44 => [4, 7, 2],
    ]
*/

So we assert that it won't reindex the array in the future...