feat: Series descriptive methods

[FBruzzesi]

Description

Similar to #159 but for series and expr methods (complete list from polars); introduces the following Series methods:

• is_duplicated
• is_empty (not in expr)
• is_unique
• null_count
• is_first_distinct
• is_last_distinct
• is_sorted (not in expr)
• value_counts (not in expr)

[FBruzzesi]

Would it make sense to dynamically extract the set of methods that a polars Series supports but Expr does not? Something like the following should be enough:

series_only = [
    i for i in dir(pl.Series)
    if not i[0].isupper() and i[0] != "_" and i not in dir(pl.Expr)
]

Let me know what you think

[MarcoGorelli]

maybe, but there's also value in this being manual, so we can inspect whether it makes sense that a given method is missing

[MarcoGorelli]

thanks @FBruzzesi ! Looks like value_counts is failing on the minimum pandas version, possibly related to pandas-dev/pandas#49912

[FBruzzesi]

thanks @FBruzzesi ! Looks like value_counts is failing on the minimum pandas version, possibly related to pandas-dev/pandas#49912

Thanks Marco, it seems that both naming and order is different (as if sort=True has no effect?). Should we manually address that? E.g. renaming and sorting afterwards?

[MarcoGorelli]

I think order is fine, there are other places where the order isn't preserved (e.g. group_by) - shall we just document the lack of ordering guarantee, and fixup the names?

[FBruzzesi]

Pandas value_counts has a sort keyword since forever I think (v1.0 is the furthest I could find on the doc page). Setting sort=True and getting unsorted results is not ideal to me

[MarcoGorelli]

yeah, sorry, hadn't looked carefully enough - sure, this one should be easy enough to work around and manually fixup

[MarcoGorelli]

Wow, absolute legend mate!

I can never remember the is_first_distinct in pandas, so I may need to refer to this if I ever need to write pandas again (and I probably will at some point 😄 )

Just made a minor comment

Approving, though I didn't sleep much tonight (got up early to catch a train) so I'm not super-"with it", feel free to merge if you're confident

[MarcoGorelli]

if self._series.name is something like 0 or '', will this overwrite it with 'index'? should be specifically check for if self._series.name is None?

[FBruzzesi]

Thanks! That's a great catch 🙈