Support mean for bool columns in DataFrame.Describe and Series.Describe

[taki-mekhalfa]

Fixes: #13735

I Had to use str_value from Series to ensure we have the same representation for non numerical columns (the float representing the mean for bool columns). This means that mean for bools are printed the same ways as for other columns and will respect the polars.Config.set_fmt_float

True and False become true and false to be consistent with what happens when you just print df; but it's easily changeable.

If we only use str(v):

shape: (9, 7)
┌────────────┬──────────┬──────────┬────────────────────┬──────┬──────┬────────────┐
│ describe   ┆ a        ┆ b        ┆ c                  ┆ d    ┆ e    ┆ f          │
│ ---        ┆ ---      ┆ ---      ┆ ---                ┆ ---  ┆ ---  ┆ ---        │
│ str        ┆ f64      ┆ f64      ┆ str                ┆ str  ┆ str  ┆ str        │
╞════════════╪══════════╪══════════╪════════════════════╪══════╪══════╪════════════╡
│ count      ┆ 3.0      ┆ 2.0      ┆ 3                  ┆ 2    ┆ 2    ┆ 3          │
│ null_count ┆ 0.0      ┆ 1.0      ┆ 0                  ┆ 1    ┆ 1    ┆ 0          │
│ mean       ┆ 2.266667 ┆ 4.5      ┆ 0.6666666666666666 ┆ null ┆ null ┆ null       │
│ std        ┆ 1.101514 ┆ 0.707107 ┆ null               ┆ null ┆ null ┆ null       │
│ min        ┆ 1.0      ┆ 4.0      ┆ False              ┆ b    ┆ null ┆ 2020-01-01 │
│ 25%        ┆ 2.8      ┆ 4.0      ┆ null               ┆ null ┆ null ┆ null       │
│ 50%        ┆ 2.8      ┆ 5.0      ┆ null               ┆ null ┆ null ┆ null       │
│ 75%        ┆ 3.0      ┆ 5.0      ┆ null               ┆ null ┆ null ┆ null       │
│ max        ┆ 3.0      ┆ 5.0      ┆ True               ┆ c    ┆ null ┆ 2022-01-01 │
└────────────┴──────────┴──────────┴────────────────────┴──────┴──────┴────────────┘

If we use str_value:

shape: (9, 7)
┌────────────┬──────────┬──────────┬──────────┬──────┬──────┬────────────┐
│ describe   ┆ a        ┆ b        ┆ c        ┆ d    ┆ e    ┆ f          │
│ ---        ┆ ---      ┆ ---      ┆ ---      ┆ ---  ┆ ---  ┆ ---        │
│ str        ┆ f64      ┆ f64      ┆ str      ┆ str  ┆ str  ┆ str        │
╞════════════╪══════════╪══════════╪══════════╪══════╪══════╪════════════╡
│ count      ┆ 3.0      ┆ 2.0      ┆ 3        ┆ 2    ┆ 2    ┆ 3          │
│ null_count ┆ 0.0      ┆ 1.0      ┆ 0        ┆ 1    ┆ 1    ┆ 0          │
│ mean       ┆ 2.266667 ┆ 4.5      ┆ 0.666667 ┆ null ┆ null ┆ null       │
│ std        ┆ 1.101514 ┆ 0.707107 ┆ null     ┆ null ┆ null ┆ null       │
│ min        ┆ 1.0      ┆ 4.0      ┆ false    ┆ b    ┆ null ┆ 2020-01-01 │
│ 25%        ┆ 2.8      ┆ 4.0      ┆ null     ┆ null ┆ null ┆ null       │
│ 50%        ┆ 2.8      ┆ 5.0      ┆ null     ┆ null ┆ null ┆ null       │
│ 75%        ┆ 3.0      ┆ 5.0      ┆ null     ┆ null ┆ null ┆ null       │
│ max        ┆ 3.0      ┆ 5.0      ┆ true     ┆ c    ┆ null ┆ 2022-01-01 │
└────────────┴──────────┴──────────┴──────────┴──────┴──────┴────────────┘

If we change config:

with pl.Config(set_fmt_float="full"):
    print(df.describe())

shape: (9, 7)
┌────────────┬────────────────────┬────────────────────┬────────────────────┬──────┬──────┬────────────┐
│ describe   ┆ float              ┆ int                ┆ bool               ┆ str  ┆ str2 ┆ date       │
│ ---        ┆ ---                ┆ ---                ┆ ---                ┆ ---  ┆ ---  ┆ ---        │
│ str        ┆ f64                ┆ f64                ┆ str                ┆ str  ┆ str  ┆ str        │
╞════════════╪════════════════════╪════════════════════╪════════════════════╪══════╪══════╪════════════╡
│ count      ┆ 3                  ┆ 2                  ┆ 3                  ┆ 2    ┆ 2    ┆ 3          │
│ null_count ┆ 0                  ┆ 1                  ┆ 0                  ┆ 1    ┆ 1    ┆ 0          │
│ mean       ┆ 2.2666666666666666 ┆ 4.5                ┆ 0.6666666666666666 ┆ null ┆ null ┆ null       │
│ std        ┆ 1.1015141094572205 ┆ 0.7071067811865476 ┆ null               ┆ null ┆ null ┆ null       │
│ min        ┆ 1                  ┆ 4                  ┆ false              ┆ b    ┆ eur  ┆ 2020-01-01 │
│ 25%        ┆ 2.8                ┆ 4                  ┆ null               ┆ null ┆ null ┆ null       │
│ 50%        ┆ 2.8                ┆ 5                  ┆ null               ┆ null ┆ null ┆ null       │
│ 75%        ┆ 3                  ┆ 5                  ┆ null               ┆ null ┆ null ┆ null       │
│ max        ┆ 3                  ┆ 5                  ┆ true               ┆ c    ┆ usd  ┆ 2022-01-01 │
└────────────┴────────────────────┴────────────────────┴────────────────────┴──────┴──────┴────────────┘

[Wainberg]

I think the underlying issue should be fixed by #13725, right?

[taki-mekhalfa]

I think the underlying issue should be fixed by #13725, right?

Sorry what issue? float display?

[taki-mekhalfa]

I went ahead and added mean for bool series too;

>>> s = pl.Series([True, False, True, None, True])
>>> s.describe()
shape: (4, 2)
┌────────────┬───────┐
│ statistic  ┆ value │
│ ---        ┆ ---   │
│ str        ┆ f64   │
╞════════════╪═══════╡
│ count      ┆ 4.0   │
│ null_count ┆ 1.0   │
│ sum        ┆ 3.0   │
│ mean       ┆ 0.75  │
└────────────┴───────┘

[taki-mekhalfa]

This is already being addressed here: #13720. Closing.