Series.from_list/2 throws argument error when opts != [] in some cases

[kylewhite21]

In many cases casting to a series and converting the data type in one shot fails, but converting to a series and then casting works. I'm not rusty enough to know why.

iex(2)> S.from_list([1, 2], dtype: :string)
** (ArgumentError) argument error
    (explorer 0.9.2) Explorer.PolarsBackend.Native.s_from_list_str("", [1, 2])
    (explorer 0.9.2) lib/explorer/polars_backend/series.ex:24: Explorer.PolarsBackend.Series.from_list/2
    iex:2: (file)

iex(2)> S.from_list([1, 2]) |> S.cast(:string)
#Explorer.Series<
  Polars[2]
  string ["1", "2"]
>

other examples:

alias Explorer.Series, as: S

# opts != [] errors
S.from_list(["1", "2"], dtype: {:u, 16})
S.from_list(["1", "2"]) |> S.cast({:u, 16})

# opts != [] errors
S.from_list([1.5, 2.5], dtype: {:u, 16})
S.from_list([1.5, 2.5]) |> S.cast({:u, 16})

# both work
S.from_list([1, 2], dtype: {:f, 32})
S.from_list([1, 2]) |> S.cast({:f, 32})

[josevalim]

Yes, this is expected. from_list mostly does not perform casting except few cases (like ints/floats), you must pass the exact data type. That's because it is very hard and expensive to do the casting at that level. Once you have the data structure in memory and you know exactly what it looks like, it is much easier.

[kylewhite21]

Got it, thanks for the fast reply!

[josevalim]

Fantatic, and i pushed some docs to avoid future confusion!