<prepare-dataframe-and-fit-transform>
>>> train_df = pl.DataFrame({"fruits": [
...     "apple",
...     "apple",
...     "banana",
...     "banana",
...     "banana",
...     "cherry",
... ]})
>>> encoder = sk.CountEncoder()
>>> encoder.fit_transform(train_df)
shape: (6, 1)
┌────────┐
│ fruits │
│ ---    │
│ i64    │
╞════════╡
│ 2      │
│ 2      │
│ 3      │
│ 3      │
│ 3      │
│ 1      │
└────────┘
</prepare-dataframe-and-fit-transform>
