Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:120463
MIME-Version: 1.0
References: <289E585B-EF8B-4B17-89BE-BE8295FD9FE1@gmail.com>
 <CAB-BujYyz4vFAmi+OKi0rjqViE02eUjDpkkYyAMRCf10t8mNXA@mail.gmail.com>
 <4CA1668E-A342-452E-A994-5839C377CB27@gmail.com> <CAB-BujY2f3tM5CwRVAuVj962iC_9K=1X1A0at2QVdORxQDqx3A@mail.gmail.com>
In-Reply-To: <CAB-BujY2f3tM5CwRVAuVj962iC_9K=1X1A0at2QVdORxQDqx3A@mail.gmail.com>
Date: Tue, 30 May 2023 18:25:21 +0200
Message-ID: <CAB-Bujbuk+4bXQ-PfCxgtxNd_yvJ6PUJVO4GxsmTFB3vqUFiKw@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)

Here we go,
https://3v4l.org/KsL3o


function array_group(array $arr1, callable $compare): array {
    $groups = [];
    $group = [];
    $prev = NULL;
    foreach ($arr1 as $value) {
        if ($group && !$compare($prev, $value)) {
            $groups[] = $group;
            $group = [];
        }
        $group[] = $value;
        $prev = $value;
    }
    if ($group) {
        $groups[] = $group;
    }
    return $groups;
}

On Tue, 30 May 2023 at 18:21, Andreas Hennings <andreas@dqxtech.net> wrote:
>
> Thank you, this clarifies and it confirms my initial assumption of
> what you are proposing.
> So you want to slice an array by comparing adjacent values.
>
>
> My personal feedback:
> I think the need for the grouping behavior you describe is not common
> enough that it needs its own native function.
> 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.
>
> Your behavior can be implemented in userland like so:
> https://3v4l.org/epvHm
>
>
> $arr1 = array(1,2,2,3,1,2,0,4,5,2);
>
> $groups = [];
> $group = [];
> $prev = NULL;
> foreach ($arr1 as $value) {
>     if ($group && $prev > $value) {
>         $groups[] = $group;
>         $group = [];
>     }
>     $group[] = $value;
>     $prev = $value;
> }
> if ($group) {
>     $groups[] = $group;
> }
>
> print_r($groups);
>
>
> If needed, the comparison function can be separated out and passed as
> a parameter.
> So the array_group() function with a comparison callback parameter can
> be implemented in userland.
>
> I think you need to make a case as to why the behavior you describe
> justifies a native function.
> 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
> > >>
> >