column_associations#

skrub.column_associations(df)[source]#

Get measures of statistical associations between all pairs of columns.

At the moment, the only reported metric is Cramer’s V statistic. More may be added in the future.

The result is returned as a dataframe with columns:

['left_column_name', 'left_column_idx', 'right_column_name', 'right_column_idx', 'cramer_v']

As the function is commutative, each pair of columns appears only once (either col_1, col_2 or col_2, col_1 but not both). The results are sorted from most associated to least associated.

To compute the Cramer’s V statistic, all columns are discretized. Numeric columns are binned with 10 bins. For categorical columns, only the 10 most frequent categories are considered. In both cases, nulls are treated as a separate category, ie a separate row in the contingency table. Thus associations between the values of 2 columns or between their missingness patterns may be captured.

Parameters:

dfdataframe: The dataframe whose columns will be compared to each other.

Returns:

dataframe: The computed associations.

Notes

Cramér’s V is a measure of association between two nominal variables, giving a value between 0 and +1 (inclusive).

Cramer’s V

Examples

>>> import numpy as np
>>> import pandas as pd
>>> import skrub
>>> pd.set_option('display.width', 200)
>>> pd.set_option('display.max_columns', 10)
>>> pd.set_option('display.precision', 4)
>>> rng = np.random.default_rng(33)
>>> df = pd.DataFrame({f"c_{i}": rng.random(size=20)*10 for i in range(5)})
>>> df["c_str"] = [f"val {i}" for i in range(df.shape[0])]
>>> df.shape
(20, 6)
>>> df.head()
      c_0     c_1     c_2     c_3     c_4  c_str
0  4.4364  4.0114  6.9271  7.0970  4.8913  val 0
1  5.6849  0.7192  7.6430  4.6441  2.5116  val 1
2  9.0810  9.4011  1.9257  5.7429  6.2358  val 2
3  2.5425  2.9678  9.7801  9.9879  6.0709  val 3
4  5.8878  9.3223  5.3840  7.2006  2.1494  val 4
>>> associations = skrub.column_associations(df)
>>> associations 
   left_column_name  left_column_idx right_column_name  right_column_idx  cramer_v
0               c_3                3             c_str                 5    0.8215
1               c_1                1               c_4                 4    0.8215
2               c_0                0               c_1                 1    0.8215
3               c_2                2             c_str                 5    0.7551
4               c_0                0             c_str                 5    0.7551
5               c_0                0               c_3                 3    0.7551
6               c_1                1               c_3                 3    0.6837
7               c_0                0               c_4                 4    0.6837
8               c_4                4             c_str                 5    0.6837
9               c_3                3               c_4                 4    0.6053
10              c_2                2               c_3                 3    0.6053
11              c_1                1             c_str                 5    0.6053
12              c_0                0               c_2                 2    0.6053
13              c_2                2               c_4                 4    0.5169
14              c_1                1               c_2                 2    0.4122
>>> pd.reset_option('display.width')
>>> pd.reset_option('display.max_columns')
>>> pd.reset_option('display.precision')