Add Series.index_of

[fizzlebert]

I wanted to use the index_of in elixir so here's my implementation. My rust skills are lacking but I tried, so please let me know if anything needs fixing. I'm not super happy with the inconsistent error messages for mismatching types but if there's a better way I'm happy to change it.

[billylanchantin]

Sorry, this fell off my radar.

Thanks for the addition! Seems quite handy.

I'm not super happy with the inconsistent error messages for mismatching types but if there's a better way I'm happy to change it.

Did you have any more ideas?

One thought is to try and make a singleton series first in Elixir with the known dtype. If that fails because of a dtype mismatch, then we can fail with a consistent error message. If not, we can pass along both series. As a bonus, we won't need to do any additional casting in Rust.

So something like this:

  def index_of(series, value) do
    value_series =
      try do
        from_list([value], series.dtype)
      catch
        # ...
      end

    apply_series(series, :index_of, [value_series])
  end

If this approach doesn't work well, then I think the mismatched error messages are acceptable (if not ideal).

[fizzlebert]

Sorry I didn't see the notification till now and thanks for your suggestion that's a much nicer solution. I found implementing it results in odd behaviour for series of type duration as it does not cast values to different precision like Series.member?. So I added extra specific handling for durations to cast them to the correct type and raise an error if index_of is called on a series of duration without a duration value.

[billylanchantin]

Excellent! I agree this solution is much nicer.

I've requested one additional comment to explain the {:duration, _} thing, then this is good to go.

[billylanchantin]

Excellent work, @fizzlebert! Thank you for the addition!

[fizzlebert]

I just realised this should have a return type of integer() | nil not just integer(). I can make a new pr for it if you think it's necessary.

[billylanchantin]

No that's ok, I'll just change it. Thanks for letting us know!