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Date: Tue, 30 May 2023 18:33:50 +0200
Message-ID: <CAB-BujYgoMVBgTYfgK+iQKyFB0HGGjQkdyV6e8o8=1KwV5mdzw@mail.gmail.com>
To: Boro Sitnikovski <buritomath@gmail.com>
Cc: internals@lists.php.net
Content-Type: text/plain; charset="UTF-8"
Subject: Re: [PHP-DEV] [RFC] [Discussion] Add new function `array_group`
From: andreas@dqxtech.net (Andreas Hennings)

On Tue, 30 May 2023 at 18:27, Boro Sitnikovski <buritomath@gmail.com> wrote:
>
> Hi,
>
> Thank you for your thoughts.
>
> > I would say the more common desired behavior is the one in your first
> > example. And even for that we don't have a native function.
>
> This Google search might give more insight into the number of discussions about a grouping functionality: https://www.google.com/search?q=php+group+elements+site:stackoverflow.com

All of the examples I looked at are asking for the first kind of
grouping, that can be implemented as in your first example.
In all the examples, if two items are equal, they end up in the same group.

In your proposed behavior, equal items can end up in distinct groups
depending on their original position in the source array.
I don't see any questions or examples that ask for this.

-- Andreas

>
> > Your behavior can be implemented in userland like so:
> > https://3v4l.org/epvHm
>
> Correct, but then again, we can also implement `array_map`/`array_filter`/etc. in userland :)
>
> > I think you need to make a case as to why the behavior you describe
> > justifies a native function.
>
> Similar to my previous answer, but also in general - ease of access and also performance.
>
> > E.g. if you find a lot of public php code that does this kind of grouping.
> >
> > I personally suspect it is not that common.
> >
> > Cheers
> > Andreas
> >
> >
> > On Tue, 30 May 2023 at 17:08, Boro Sitnikovski <buritomath@gmail.com> wrote:
> >>
> >> 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_manual_group-php
> >> 2. The second example corresponds to https://gist.github.com/bor0/b5f449bfe85440d96abd933b9f03b310#file-test_array_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_array_incr_subseqs-php
> >>
> >> Best,
> >>
> >> Boro
> >>
> >>> On 30.5.2023, at 16:57, Andreas Hennings <andreas@dqxtech.net> wrote:
> >>>
> >>> 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.
> >>>
> >>> Cheers
> >>> Andreas
> >>>
> >>> On Tue, 30 May 2023 at 13:35, Boro Sitnikovski <buritomath@gmail.com> wrote:
> >>>>
> >>>> Hello all,
> >>>>
> >>>> As per the How To Create an RFC instructions, I am sending this e-mail in order to get your feedback on my proposal.
> >>>>
> >>>> 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.
> >>>>
> >>>> For some background as to why - usually, when people want to do grouping in PHP, they use hash maps, so something like:
> >>>>
> >>>> ```
> >>>> <?php
> >>>> $array = [
> >>>> [ 'id' => 1, 'value' => 'foo' ],
> >>>> [ 'id' => 1, 'value' => 'bar' ],
> >>>> [ 'id' => 2, 'value' => 'baz' ],
> >>>> ];
> >>>>
> >>>> $groups = [];
> >>>> foreach ( $array as $element ) {
> >>>>   $groups[ $element['id'] ][] = $element;
> >>>> }
> >>>>
> >>>> var_dump( $groups );
> >>>> ```
> >>>>
> >>>> This can now be achieved as follows (not preserving keys):
> >>>>
> >>>> ```
> >>>> <?php
> >>>> $array = [
> >>>> [ 'id' => 1, 'value' => 'foo' ],
> >>>> [ 'id' => 1, 'value' => 'bar' ],
> >>>> [ 'id' => 2, 'value' => 'baz' ],
> >>>> ];
> >>>>
> >>>> $groups = array_group( $array, function( $a, $b ) {
> >>>> return $a['id'] == $b['id'];
> >>>> } );
> >>>> ```
> >>>>
> >>>> 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.
> >>>>
> >>>> In any case, I think a utility function such as `array_group` will be widely useful.
> >>>>
> >>>> Please find attached a patch with a proposed implementation. Curious about your feedback.
> >>>>
> >>>> Best,
> >>>>
> >>>> Boro Sitnikovski
> >>>>
> >>
>