feat: add keep_column[s] params to to_dummies

[mcrumiller]

Resolves #14831.

Was fairly easy to implement so no harm if rejected. Not super happy about the different parameter names for Series and DataFrame, any suggested alternatives? keep_original would work but sounds ugly to me.

>>> import polars as pl
>>> pl.Series("a", [1, 2, 3]).to_dummies(keep_column=True)
shape: (3, 4)
┌─────┬─────┬─────┬─────┐
│ a   ┆ a_1 ┆ a_2 ┆ a_3 │
│ --- ┆ --- ┆ --- ┆ --- │
│ i64 ┆ u8  ┆ u8  ┆ u8  │
╞═════╪═════╪═════╪═════╡
│ 1   ┆ 1   ┆ 0   ┆ 0   │
│ 2   ┆ 0   ┆ 1   ┆ 0   │
│ 3   ┆ 0   ┆ 0   ┆ 1   │
└─────┴─────┴─────┴─────┘

>>> pl.DataFrame({"a": [1, 2], "b": [3, 4]}).to_dummies(keep_columns=True)
shape: (2, 6)
┌─────┬─────┬─────┬─────┬─────┬─────┐
│ a   ┆ a_1 ┆ a_2 ┆ b   ┆ b_3 ┆ b_4 │
│ --- ┆ --- ┆ --- ┆ --- ┆ --- ┆ --- │
│ i64 ┆ u8  ┆ u8  ┆ i64 ┆ u8  ┆ u8  │
╞═════╪═════╪═════╪═════╪═════╪═════╡
│ 1   ┆ 1   ┆ 0   ┆ 3   ┆ 1   ┆ 0   │
│ 2   ┆ 0   ┆ 1   ┆ 4   ┆ 0   ┆ 1   │
└─────┴─────┴─────┴─────┴─────┴─────┘

[mcrumiller]

Unsure why code coverage failed, I added coverage tests.

[s-banach]

What happens if one of the new dummy columns has the same name as the original column?

[mcrumiller]

What happens if one of the new dummy columns has the same name as the original column?

That would have to be very contrived. The dummy columns are named by [original_name]_[value]. One would have to have explicitly already had a column with that name, and that issue is present on the existing implementation anyway:

import polars as pl

df = pl.DataFrame({
    "a": [1, 2, 3],
    "a_1": [1, 2, 3],
})
df.to_dummies("a")

polars.exceptions.DuplicateError: unable to hstack, column with name "a_1" already exists

My guess is that one can contrive many scenarios to collide with polars' renaming, but it's not in our best interest to fight those edge cases.

[s-banach]

As long as it raises the same error.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.19%. Comparing base (dcee934) to head (b56daed).
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #14844      +/-   ##
==========================================
+ Coverage   81.14%   81.19%   +0.04%     
==========================================
  Files        1363     1367       +4     
  Lines      175282   175326      +44     
  Branches     2527     2527              
==========================================
+ Hits       142236   142350     +114     
+ Misses      32568    32496      -72     
- Partials      478      480       +2     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.