narwhals.Series.cat

get_categories()

Get unique categories from column.

Returns:

Type	Description
SeriesT	A new Series containing the unique categories.

Examples:

Let's create some series:

>>> import pandas as pd
>>> import polars as pl
>>> import pyarrow as pa
>>> import narwhals as nw
>>> from narwhals.typing import IntoSeriesT

>>> data = ["apple", "mango", "mango"]
>>> s_pd = pd.Series(data, dtype="category")
>>> s_pl = pl.Series(data, dtype=pl.Categorical)
>>> s_pa = pa.chunked_array([data]).dictionary_encode()

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

>>> def agnostic_get_categories(s_native: IntoSeriesT) -> IntoSeriesT:
...     s = nw.from_native(s_native, series_only=True)
...     return s.cat.get_categories().to_native()

We can then pass any supported library such as pandas, Polars, or PyArrow to agnostic_get_categories:

>>> agnostic_get_categories(s_pd)
0    apple
1    mango
dtype: object

>>> agnostic_get_categories(s_pl)
shape: (2,)
Series: '' [str]
[
   "apple"
   "mango"
]

>>> agnostic_get_categories(s_pa)
<pyarrow.lib.ChunkedArray object at ...>
[
  [
    "apple",
    "mango"
  ]
]