CountFrequencyEncoder

class feature_engine.encoding.CountFrequencyEncoder(encoding_method='count', variables=None, missing_values='raise', ignore_format=False, unseen='ignore')

The CountFrequencyEncoder() replaces categories by either the count or the percentage of observations per category.

For example in the variable colour, if 10 observations are blue, blue will be replaced by 10. Alternatively, if 10% of the observations are blue, blue will be replaced by 0.1.

The CountFrequencyEncoder() will encode only categorical variables by default (type ‘object’ or ‘categorical’). You can pass a list of variables to encode. Alternatively, the encoder will find and encode all categorical variables (type ‘object’ or ‘categorical’).

With ignore_format=True you have the option to encode numerical variables as well. The procedure is identical, you can either enter the list of variables to encode, or the transformer will automatically select all variables.

The encoder first maps the categories to the counts or frequencies for each variable (fit). The encoder then replaces the categories with those numbers (transform).

More details in the User Guide.

Parameters

encoding_method: str, default=’count’

Desired method of encoding.

‘count’: number of observations per category

‘frequency’: percentage of observations per category

variables: list, default=None

The list of categorical variables that will be encoded. If None, the encoder will find and transform all variables of type object or categorical by default. You can also make the transformer accept numerical variables, see the parameter ignore_format.

missing_values: string, default=’raise’

Indicates if missing values should be ignored or raised. If 'raise' the transformer will return an error if the the datasets to fit or transform contain missing values. If 'ignore', missing data will be ignored when learning parameters or performing the transformation.

ignore_format: bool, default=False

This transformer operates only on variables of type object or categorical. To override this behaviour and allow the transformer to transform numerical variables as well, set to True.

If ignore_format is False, the encoder will automatically select variables of type object or categorical, or check that the variables entered by the user are of type object or categorical. If True, the encoder will select all variables or accept all variables entered by the user, including those cast as numeric.

In short, set to True when you want to encode numerical variables.

unseen: string, default=’ignore’

Indicates what to do when categories not present in the train set are encountered during transform. If 'raise', then unseen categories will raise an error. If 'ignore', then unseen categories will be encoded as NaN and a warning will be raised instead. If 'encode', unseen categories will be encoded as 0 (zero).

Attributes

encoder_dict_:

Dictionary with the count or frequency per category, per variable.

variables_:

The group of variables that will be transformed.

feature_names_in_:

List with the names of features seen during fit.

n_features_in_:

The number of features in the train set used in fit.

See also

feature_engine.encoding.RareLabelEncoder

category_encoders.count.CountEncoder

Notes

NAN will be introduced when encoding categories that were not present in the training set. If this happens, try grouping infrequent categories using the RareLabelEncoder(), or set unseen='encode'.

There is a similar implementation in the open-source package Category encoders

Examples

>>> import pandas as pd
>>> from feature_engine.encoding import CountFrequencyEncoder
>>> X = pd.DataFrame(dict(x1 = [1,2,3,4], x2 = ["c", "a", "b", "c"]))
>>> cf = CountFrequencyEncoder(encoding_method='count')
>>> cf.fit(X)
>>> cf.transform(X)
   x1  x2
0   1   2
1   2   1
2   3   1
3   4   2

>>> cf = CountFrequencyEncoder(encoding_method='frequency')
>>> cf.fit(X)
>>> cf.transform(X)
   x1    x2
0   1  0.50
1   2  0.25
2   3  0.25
3   4  0.50

Methods

fit:	Learn the count or frequency per category, per variable.
fit_transform:	Fit to data, then transform it.
get_feature_names_out:	Get output feature names for transformation.
get_params:	Get parameters for this estimator.
set_params:	Set the parameters of this estimator.
inverse_transform:	Convert the data back to the original representation.
transform:	Encode the categories to numbers.

fit(X, y=None)

Learn the counts or frequencies which will be used to replace the categories.

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: pandas Series, default = None

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

fit_transform(X, y=None, **fit_params)

Fit to data, then transform it.

Fits transformer to X and y with optional parameters fit_params and returns a transformed version of X.

Parameters

Xarray-like of shape (n_samples, n_features)

Input samples.

yarray-like of shape (n_samples,) or (n_samples, n_outputs), default=None

Target values (None for unsupervised transformations).

**fit_paramsdict

Additional fit parameters.

Returns

X_newndarray array of shape (n_samples, n_features_new)

Transformed array.

get_feature_names_out(input_features=None)

Get output feature names for transformation. In other words, returns the variable names of transformed dataframe.

Parameters

input_featuresarray or list, default=None

This parameter exits only for compatibility with the Scikit-learn pipeline.

• If None, then feature_names_in_ is used as feature names in.

• If an array or list, then input_features must match feature_names_in_.

Returns

feature_names_out: list

Transformed feature names.

rtype

List[Union[str, int]] ..

get_params(deep=True)

Get parameters for this estimator.

Parameters

deepbool, default=True

If True, will return the parameters for this estimator and contained subobjects that are estimators.

Returns

paramsdict

Parameter names mapped to their values.

inverse_transform(X)

Convert the encoded variable back to the original values.

Parameters

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

The transformed dataframe.

Returns

X_tr: pandas dataframe of shape = [n_samples, n_features].

The un-transformed dataframe, with the categorical variables containing the original values.

rtype

DataFrame ..

set_params(**params)

Set the parameters of this estimator.

The method works on simple estimators as well as on nested objects (such as Pipeline). The latter have parameters of the form <component>__<parameter> so that it’s possible to update each component of a nested object.

Parameters

**paramsdict

Estimator parameters.

Returns

selfestimator instance

Estimator instance.

transform(X)

Replace categories with the learned parameters.

Parameters

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

The dataset to transform.

Returns

X_new: pandas dataframe of shape = [n_samples, n_features].

The dataframe containing the categories replaced by numbers.

rtype

DataFrame ..