Function proposal - at/get()

[marcospassos]

We have a use case where we need to get a value by its index.

In that sense, I'd like to suggest introducing a function at/get(iterable $iterable, int $index) : ?int that takes an iterable and returns the item at the specified index.

I'll be glad to provide a PR if welcome.

[marcospassos]

Alternatively, we can introduce a seek(iterable $iterable, int $index) : \Iterator, that takes an iterable and returns an iterator at the specified index. The advantages of this approach are iteration deferring on non-seekable iterators and support for both key and value lookup.

[SamMousa]

Isn't this covered by slice?

slice($iterable, 15, 1)

[dakujem]

@marcospassos It would not be feasible to use int for the $index because the keys yielded by generators can be of any type (see https://3v4l.org/N5VPI)

@SamMousa Slice does not cover the case, because 1. it returns an array and not the element, 2. it works with element order in the iterable and not indexes of the elements in the iterable.

The search function can be altered to also pass the key to the predicate, then it is simple to create an at/get function that searches for an element by a given key.

function searchWithKeys(iterable $input, callable $predicate): mixed
{
    foreach ($input as $key => $value) {
        if ($predicate($value, $key)) {
            return $value;
        }
    }
    // Handle this case as you see fit
    return null;
}

function at(iterable $input, mixed $index): mixed
{
    return searchWithKeys($input, fn(mixed $v, mixed $k): bool => $k === $index);
}

P.S. late to the party, but adding this to the reference for future use.

[SamMousa]

1. it returns an array and not the element,

This a detail that is solvable.

2. it works with element order in the iterable and not indexes of the elements in the iterable.

The definition of index implies it is about order. If you mean keys of the elements in the iterable that's a different thing. But then I get what you mean.

An implementation with current code would look like this:

function filterKeys(iterable $input, mixed $key): iterable {
    return fromPairs(filter(fn($kv) => $kv[0] === $key, toPairs($input))));
}

I'm not opposed to having this in the library btw, just noticing that it doesn't add much as the userland implementation isn't that complicated.

[dakujem]

I assumed that OP wanted a "find by key" method, not "find by by sequence number" (i.e. "get second element of the iterable collection"). For that, slice would work, true. I'm editing my answer above to clarify what I meant.