That's like saying someone would use this:
$result = $arr |> fn($x) => array_column($x, 'tags') |> fn($x) => array_merge(...$x) |> array_unique(...) |> array_values(...)
which is harder to reason about than the nested functions. array_values( array_unique( array_merge( ...array_column($arr, 'tags') ) ) );
or array_values(
array_unique(
array_merge(
...array_column($arr, 'tags')
)
)
);