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Date: Wed, 31 May 2023 22:59:51 +0000
To: "php internals" <internals@lists.php.net>
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Subject: Re: [PHP-DEV] Re: [RFC] [Discussion] Add new function `array_group`
From: larry@garfieldtech.com ("Larry Garfield")

On Wed, May 31, 2023, at 10:47 PM, Boro Sitnikovski wrote:

> 1. The grouping that JavaScript/.NET/Lodash/Scala/etc. do (this should 
> be the default of `array_group`)
> 2. The grouping that Haskell does, the one I proposed earlier (this can 
> be altered in a flag within `array_group`)
>
> Based on this, I'd like to adjust my initial proposal, where we would 
> have the following function: `function array_group(array $array, 
> callable $callback, bool $consecutive_pairs = false): array {}`
>
> If the argument `consecutive_pairs` is false, it will use the 
> function's return value to do the grouping ($callback accepting single 
> element in this case)
> Otherwise, it will use the function's boolean return value to check if 
> two consecutive elements need to be grouped ($callback accepting two 
> elements in this case)
>
> (This approach seems to be consistent with `array_filter` in the sense 
> the callback accepts one or two arguments)
>
> With a few example usages:
>
> ```
> var_dump( array_group($arr1, function( $x ) {
> return (string) strlen( $x );
> } ) );
> // Producing ['3' => ['one', 'two'], '5' => ['three']]
> ```
>
> Another one:
>
> ```
> $arr = [-1,2,-3,-4,2,1,2,-3,1,1,2];
>
> $groups = array_group( $arr, function( $p1, $p2 ) {
>   return ($p1 > 0) == ($p2 > 0);
> } );
> // Producing [[-1],[2],[-3,-4],[2,1,2],[-3],[1,1,2]]
> ```

This sounds like two separate functions in a trenchcoat.  It should be two separate functions.

> I believe this proposal captures many use cases, beyond the examples we 
> discussed. Curious about any other thoughts.
>
> I'm also attaching a PoC patch that implements this.
>
> Attachments:
> * array_group.patch

Side note: I don't think anyone reads patches sent to the list.  I didn't even realize it allowed attachments. :-)  If you want someone to review code, a GitHub PR is the way to go.

You can also include benchmarks there.  From experience, if you don't have a compelling reason why this *needs* to be in C rather than PHP (which in this case boils down to performance exclusively), you're not going to be able to convince people to add another random utility function.  That's just the reality these days.

--Larry Garfield