Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:120474
Content-Type: text/plain;
	charset=us-ascii
Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3731.600.7\))
In-Reply-To: <CAB-BujYgoMVBgTYfgK+iQKyFB0HGGjQkdyV6e8o8=1KwV5mdzw@mail.gmail.com>
Date: Tue, 30 May 2023 19:24:51 +0200
Cc: internals@lists.php.net
Content-Transfer-Encoding: quoted-printable
Message-ID: <9D69B8D4-835A-47C0-A3BD-64285849BB02@gmail.com>
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>
 <B35AAF0F-B899-4771-AAFD-1109BE7A9B7D@gmail.com>
 <CAB-BujYgoMVBgTYfgK+iQKyFB0HGGjQkdyV6e8o8=1KwV5mdzw@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)

Hi,

> On 30.5.2023, at 18:33, Andreas Hennings <andreas@dqxtech.net> wrote:
>=20
> On Tue, 30 May 2023 at 18:27, Boro Sitnikovski <buritomath@gmail.com> =
wrote:
>>=20
>> Hi,
>>=20
>> Thank you for your thoughts.
>>=20
>>> 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.
>>=20
>> This Google search might give more insight into the number of =
discussions about a grouping functionality: =
https://www.google.com/search?q=3Dphp+group+elements+site:stackoverflow.co=
m
>=20
> 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.
>=20
> 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.

This is correct, although, if the array is sorted initially (and =
depending on which operation and what we want to do), we can still solve =
the same problem by using equality check.

The idea is that `array_group` is more general since it works with =
operators other than `=3D=3D`, whereas the hashmap approach is only =
limited to equality check.

A good illustration of this is the increasing subsequences problem, or =
any other problem of similar nature.

Here's some more examples:

1. Use `array_group` to create list of singleton list:
```
$groups =3D array_group( $arr, function( $p1, $p2 ) {
  return false;
} );
```

(This can also be achieved with `array_map` returning `[ $x ]`)

2. Distinct groups for consecutive positive and negative elements

```
$arr =3D [-1,2,-3,-4,2,1,2,-3,1,1,2];

$groups =3D array_group( $arr, function( $p1, $p2 ) {
  return ($p1 > 0) =3D=3D ($p2 > 0);
} );
```

This produces `[[-1],[2],[-3,-4],[2,1,2],[-3],[1,1,2]]`, so we can =
easily capture the groups of highs/lows for example.

3. Group sentences (similar to `explode`, but still different)

```
$arr =3D "Hello, PHP. Good to see you.";
$groups =3D array_group( str_split( $arr ), function( $p1, $p2 ) {
	return '.' !=3D=3D $p1;
} );

$groups =3D array_map( 'join', $groups );
```

Producing `[ "Hello, PHP.", " Good to see you." ]`.

4. Grouping book sections
```
$book_sections =3D [ '1.0', '1.1', '1.2', '2.0', '2.1', '3.0', '3.1' ];
$groups =3D array_group( $book_sections, function( $p1, $p2 ) {
	return $p1[0] =3D=3D=3D $p2[0];
} );
```

Producing `[ [ '1.0', '1.1', '1.2' ], [ '2.0', '2.1'], [ '3.0', '3.1' ] =
]`

and so on...

Basically, it's a very general utility :)

Best,

Boro


>=20
> -- Andreas
>=20
>>=20
>>> Your behavior can be implemented in userland like so:
>>> https://3v4l.org/epvHm
>>=20
>> Correct, but then again, we can also implement =
`array_map`/`array_filter`/etc. in userland :)
>>=20
>>> I think you need to make a case as to why the behavior you describe
>>> justifies a native function.
>>=20
>> Similar to my previous answer, but also in general - ease of access =
and also performance.
>>=20
>>> E.g. if you find a lot of public php code that does this kind of =
grouping.
>>>=20
>>> I personally suspect it is not that common.
>>>=20
>>> Cheers
>>> Andreas
>>>=20
>>>=20
>>> On Tue, 30 May 2023 at 17:08, Boro Sitnikovski =
<buritomath@gmail.com> wrote:
>>>>=20
>>>> Hey,
>>>>=20
>>>> Thanks for the suggestion.
>>>>=20
>>>> For the previous case in the code, I added these in a Gist to not =
clutter here too much:
>>>>=20
>>>> 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
>>>>=20
>>>> Best,
>>>>=20
>>>> Boro
>>>>=20
>>>>> 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
>>>>=20
>>=20