EqualWidthDiscretiser

API Reference

class feature_engine.discretisation.EqualWidthDiscretiser(variables=None, bins=10, return_object=False, return_boundaries=False)

The EqualWidthDiscretiser() divides continuous numerical variables into intervals of the same width, that is, equidistant intervals. Note that the proportion of observations per interval may vary.

The size of the interval is calculated as:

\[( max(X) - min(X) ) / bins\]

where bins, which is the number of intervals, should be determined by the user.

The interval limits are determined using pandas.cut(). The number of intervals in which the variable should be divided must be indicated by the user.

The EqualWidthDiscretiser() works only with numerical variables. A list of variables can be passed as argument. Alternatively, the discretiser will automatically select all numerical variables.

The EqualWidthDiscretiser() first finds the boundaries for the intervals for each variable. Then, it transforms the variables, that is, sorts the values into the intervals.

Parameters

variables: list, default=None

The list of numerical variables to transform. If None, the discretiser will automatically select all numerical type variables.

bins: int, default=10

Desired number of equal width intervals / bins.

return_object: bool, default=False

Whether the the discrete variable should be returned casted as numeric or as object. If you would like to proceed with the engineering of the variable as if it was categorical, use True. Alternatively, keep the default to False.

Categorical encoders in Feature-engine work only with variables of type object, thus, if you wish to encode the returned bins, set return_object to True.

return_boundariesbool, default=False

Whether the output should be the interval boundaries. If True, it returns the interval boundaries. If False, it returns integers.

Attributes

binner_dict_:	Dictionary with the interval limits per variable.
variables_:	The variables to be discretised.
n_features_in_:	The number of features in the train set used in fit.

See also

pandas.cut

https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.cut.html

References

1

Kotsiantis and Pintelas, “Data preprocessing for supervised leaning,” International Journal of Computer Science, vol. 1, pp. 111 117, 2006.

2

Dong. “Beating Kaggle the easy way”. Master Thesis. https://www.ke.tu-darmstadt.de/lehre/arbeiten/studien/2015/Dong_Ying.pdf

Methods

fit:	Find the interval limits.
transform:	Sort continuous variable values into the intervals.
fit_transform:	Fit to the data, then transform it.

fit(X, y=None)

Learn the boundaries of the equal width intervals / bins for each variable.

Parameters

X: pandas dataframe of shape = [n_samples, n_features]

The training dataset. Can be the entire dataframe, not just the variables to be transformed.

y: None

y is not needed in this encoder. You can pass y or None.

Returns

self

Raises

TypeError

• If the input is not a Pandas DataFrame

• If any of the user provided variables are not numerical

ValueError

• If there are no numerical variables in the df or the df is empty

• If the variable(s) contain null values

transform(X)

Sort the variable values into the intervals.

Parameters

X: pandas dataframe of shape = [n_samples, n_features]

The data to transform.

Returns

X: pandas dataframe of shape = [n_samples, n_features]

The transformed data with the discrete variables.

rtype

DataFrame ..

Raises

TypeError

If the input is not a Pandas DataFrame

ValueError

• If the variable(s) contain null values

• If the dataframe is not of the same size as the one used in fit()

Example

The EqualWidthDiscretiser() sorts the variable values into contiguous intervals of equal size. The size of the interval is calculated as:

( max(X) - min(X) ) / bins

where bins, which is the number of intervals, should be determined by the user. The transformer can return the variable as numeric or object (default = numeric).

The EqualWidthDiscretiser() works only with numerical variables. A list of variables can be indicated, or the discretiser will automatically select all numerical variables in the train set.

import numpy as np
import pandas as pd
import matplotlib.pyplot as plt
from sklearn.model_selection import train_test_split

from feature_engine.discretisation import EqualWidthDiscretiser

# Load dataset
data = data = pd.read_csv('houseprice.csv')

# Separate into train and test sets
X_train, X_test, y_train, y_test =  train_test_split(
            data.drop(['Id', 'SalePrice'], axis=1),
            data['SalePrice'], test_size=0.3, random_state=0)

# set up the discretisation transformer
disc = EqualWidthDiscretiser(bins=10, variables=['LotArea', 'GrLivArea'])

# fit the transformer
disc.fit(X_train)

# transform the data
train_t= disc.transform(X_train)
test_t= disc.transform(X_test)

disc.binner_dict_

'LotArea': [-inf,
  22694.5,
  44089.0,
  65483.5,
  86878.0,
  108272.5,
  129667.0,
  151061.5,
  172456.0,
  193850.5,
  inf],
 'GrLivArea': [-inf,
  768.2,
  1202.4,
  1636.6,
  2070.8,
  2505.0,
  2939.2,
  3373.4,
  3807.6,
  4241.799999999999,
  inf]}

# with equal width discretisation, each bin does not necessarily contain
# the same number of observations.
train_t.groupby('GrLivArea')['GrLivArea'].count().plot.bar()
plt.ylabel('Number of houses')