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In-Reply-To: <CAB-BujYyz4vFAmi+OKi0rjqViE02eUjDpkkYyAMRCf10t8mNXA@mail.gmail.com>
Date: Tue, 30 May 2023 17:08:46 +0200
Cc: internals@lists.php.net
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Message-ID: <4CA1668E-A342-452E-A994-5839C377CB27@gmail.com>
References: <289E585B-EF8B-4B17-89BE-BE8295FD9FE1@gmail.com>
 <CAB-BujYyz4vFAmi+OKi0rjqViE02eUjDpkkYyAMRCf10t8mNXA@mail.gmail.com>
To: Andreas Hennings <andreas@dqxtech.net>
Subject: Re: [PHP-DEV] [RFC] [Discussion] Add new function `array_group`
From: buritomath@gmail.com (Boro Sitnikovski)

Hey,

Thanks for the suggestion.

For the previous case in the code, I added these in a Gist to not =
clutter here too much:

1. The first example corresponds to =
https://gist.github.com/bor0/b5f449bfe85440d96abd933b9f03b310#file-test_ma=
nual_group-php
2. The second example corresponds to =
https://gist.github.com/bor0/b5f449bfe85440d96abd933b9f03b310#file-test_ar=
ray_group-php
3. Another example, addressing the problem of increasing subsequences is =
very simple with `array_group`: =
https://gist.github.com/bor0/b5f449bfe85440d96abd933b9f03b310#file-test_ar=
ray_incr_subseqs-php

Best,

Boro

> On 30.5.2023, at 16:57, Andreas Hennings <andreas@dqxtech.net> wrote:
>=20
> Hello Boro,
> I think you should include the "expected result" in your code =
examples.
> Maybe this is in your patch file, but I don't think we want to look at
> that for discussion.
>=20
> Cheers
> Andreas
>=20
> On Tue, 30 May 2023 at 13:35, Boro Sitnikovski <buritomath@gmail.com> =
wrote:
>>=20
>> Hello all,
>>=20
>> As per the How To Create an RFC instructions, I am sending this =
e-mail in order to get your feedback on my proposal.
>>=20
>> I propose introducing a function to PHP core named `array_group`. =
This function takes an array and a function and returns an array that =
contains arrays - groups of consecutive elements. This is very similar =
to Haskell's `groupBy` function.
>>=20
>> For some background as to why - usually, when people want to do =
grouping in PHP, they use hash maps, so something like:
>>=20
>> ```
>> <?php
>> $array =3D [
>> [ 'id' =3D> 1, 'value' =3D> 'foo' ],
>> [ 'id' =3D> 1, 'value' =3D> 'bar' ],
>> [ 'id' =3D> 2, 'value' =3D> 'baz' ],
>> ];
>>=20
>> $groups =3D [];
>> foreach ( $array as $element ) {
>>    $groups[ $element['id'] ][] =3D $element;
>> }
>>=20
>> var_dump( $groups );
>> ```
>>=20
>> This can now be achieved as follows (not preserving keys):
>>=20
>> ```
>> <?php
>> $array =3D [
>> [ 'id' =3D> 1, 'value' =3D> 'foo' ],
>> [ 'id' =3D> 1, 'value' =3D> 'bar' ],
>> [ 'id' =3D> 2, 'value' =3D> 'baz' ],
>> ];
>>=20
>> $groups =3D array_group( $array, function( $a, $b ) {
>> return $a['id'] =3D=3D $b['id'];
>> } );
>> ```
>>=20
>> The disadvantage of the first approach is that we are only limited to =
using equality check, and we cannot group by, say, `<` or other =
functions.
>> Similarly, the advantage of the first approach is that the keys are =
preserved, and elements needn't be consecutive.
>>=20
>> In any case, I think a utility function such as `array_group` will be =
widely useful.
>>=20
>> Please find attached a patch with a proposed implementation. Curious =
about your feedback.
>>=20
>> Best,
>>=20
>> Boro Sitnikovski
>>=20