narwhals.Expr.cat

get_categories()

Get unique categories from column.

Examples:

Let's create some dataframes:

>>> import pandas as pd
>>> import polars as pl
>>> import narwhals as nw
>>> data = {"fruits": ["apple", "mango", "mango"]}
>>> df_pd = pd.DataFrame(data, dtype="category")
>>> df_pl = pl.DataFrame(data, schema={"fruits": pl.Categorical})

We define a dataframe-agnostic function to get unique categories from column 'fruits':

>>> @nw.narwhalify
... def func(df):
...     return df.select(nw.col("fruits").cat.get_categories())

We can then pass either pandas or Polars to func:

>>> func(df_pd)
  fruits
0  apple
1  mango
>>> func(df_pl)
shape: (2, 1)
┌────────┐
│ fruits │
│ ---    │
│ str    │
╞════════╡
│ apple  │
│ mango  │
└────────┘