cardinality_below

skrub.selectors.cardinality_below(threshold)

Select columns whose cardinality (number of unique values) is (strictly) below threshold.

Null values do not count in the cardinality.

Examples

>>> from skrub import selectors as s
>>> import pandas as pd
>>> df = pd.DataFrame(
...     dict(
...         a1=[1, 1, 1, None],
...         a2=[1, 1, 2, None],
...         a2_b=[1, 1, 2, 2],
...         a3=[1, 2, 3, None],
...         a3_b=[1, 2, 3, 3],
...         a4=[1, 2, 3, 4],
...     )
... ).convert_dtypes()
>>> df
     a1    a2  a2_b    a3  a3_b  a4
0     1     1     1     1     1   1
1     1     1     1     2     2   2
2     1     2     2     3     3   3
3  <NA>  <NA>     2  <NA>     3   4
>>> s.select(df, s.cardinality_below(3))
     a1    a2  a2_b
0     1     1     1
1     1     1     1
2     1     2     2
3  <NA>  <NA>     2
>>> s.select(df, s.cardinality_below(4))
     a1    a2  a2_b    a3  a3_b
0     1     1     1     1     1
1     1     1     1     2     2
2     1     2     2     3     3
3  <NA>  <NA>     2  <NA>     3