nice feature :)

may i recommend for the 4th parameter to be more dynamic:

• an option to preserve keys from the originating array (and use them as keys in new groups)
• an option to use column value as a key in new groups

looking forward seeing this in core

@kaznovac Your first point is a good one, but I am not sure that I got your second one

@cmb69 any clues why does this test case keeps failing?

On AppVeyor, the test causes a segfault.

I liked the idea @7snovic! and I think it's a good idea to have it as another function:

1. As suggested by Uncle Bob in the clean code book, using flag parameters is not recommended.
2. And to always expect a single structure for the result of the function.
3. Also as @kaznovac suggested, the function could even grow to support more advanced features, having it as a separated function would make it more maintainable and gives us the flexibility we want.

Sorry, but why the 4th parameter is bool|null, why not only bool?

From RFC:

array_column(array $array, int|string|null $column_key, int|string|null $index_key = null, $grouping = null): array

Why not,

array_column(array $array, int|string|null $column_key, int|string|null $index_key = null, bool $grouping = false): array

Since the respective RFC has been declined, I'm closing this ticket.

Thanks for your work nonetheless!