"""Backward difference contrast encoding."""
import numpy as np
from patsy.contrasts import ContrastMatrix, Diff
from category_encoders.base_contrast_encoder import BaseContrastEncoder
__author__ = 'paulwestenthanner'
[docs]
class BackwardDifferenceEncoder(BaseContrastEncoder):
"""Backward difference contrast coding for encoding categorical variables.
Parameters
----------
verbose: int
integer indicating verbosity of the output. 0 for none.
cols: list
a list of columns to encode, if None, all string columns will be encoded.
drop_invariant: bool
boolean for whether or not to drop columns with 0 variance.
return_df: bool
boolean for whether to return a pandas DataFrame from transform
(otherwise it will be a numpy array).
handle_unknown: str
options are 'error', 'return_nan', 'value', and 'indicator'. The default is 'value'.
Warning: if indicator is used, an extra column will be added in if the transform matrix
has unknown categories. This can cause unexpected changes in dimension in some cases.
handle_missing: str
options are 'error', 'return_nan', 'value', and 'indicator'. The default is 'value'.
Warning: if indicator is used, an extra column will be added in if the transform
matrix has nan values. This can cause unexpected changes in dimension in some cases.
Example
-------
>>> from category_encoders import *
>>> import pandas as pd
>>> from sklearn.datasets import fetch_openml
>>> bunch = fetch_openml(name='house_prices', as_frame=True)
>>> display_cols = [
... 'Id',
... 'MSSubClass',
... 'MSZoning',
... 'LotFrontage',
... 'YearBuilt',
... 'Heating',
... 'CentralAir',
... ]
>>> y = bunch.target
>>> X = pd.DataFrame(bunch.data, columns=bunch.feature_names)[display_cols]
>>> enc = BackwardDifferenceEncoder(cols=['CentralAir', 'Heating']).fit(X, y)
>>> numeric_dataset = enc.transform(X)
>>> print(numeric_dataset.info())
<class 'pandas.core.frame.DataFrame'>
RangeIndex: 1460 entries, 0 to 1459
Data columns (total 12 columns):
# Column Non-Null Count Dtype
--- ------ -------------- -----
1 Id 1460 non-null float64
2 MSSubClass 1460 non-null float64
3 MSZoning 1460 non-null object
4 LotFrontage 1201 non-null float64
5 YearBuilt 1460 non-null float64
6 Heating_0 1460 non-null float64
7 Heating_1 1460 non-null float64
8 Heating_2 1460 non-null float64
9 Heating_3 1460 non-null float64
10 Heating_4 1460 non-null float64
11 CentralAir_0 1460 non-null float64
dtypes: float64(10), int64(1), object(1)
memory usage: 137.0+ KB
None
References
----------
.. [1] Contrast Coding Systems for Categorical Variables, from
https://stats.idre.ucla.edu/r/library/r-library-contrast-coding-systems-for-categorical-variables/
.. [2] Gregory Carey (2003). Coding Categorical Variables, from
http://ibgwww.colorado.edu/~carey/p5741ndir/Coding_Categorical_Variables.pdf
"""
[docs]
def get_contrast_matrix(self, values_to_encode: np.array) -> ContrastMatrix:
"""Get the contrast matrix for the backward difference encoder."""
return Diff().code_without_intercept(values_to_encode)