imblearn.ensemble
.BalancedBaggingClassifier¶

class
imblearn.ensemble.
BalancedBaggingClassifier
(base_estimator=None, n_estimators=10, max_samples=1.0, max_features=1.0, bootstrap=True, bootstrap_features=False, oob_score=False, warm_start=False, sampling_strategy='auto', replacement=False, n_jobs=1, random_state=None, verbose=0, ratio=None)[source]¶ A Bagging classifier with additional balancing.
This implementation of Bagging is similar to the scikitlearn implementation. It includes an additional step to balance the training set at fit time using a
RandomUnderSampler
.Read more in the User Guide.
 Parameters
 base_estimatorobject or None, optional (default=None)
The base estimator to fit on random subsets of the dataset. If None, then the base estimator is a decision tree.
 n_estimatorsint, optional (default=10)
The number of base estimators in the ensemble.
 max_samplesint or float, optional (default=1.0)
The number of samples to draw from X to train each base estimator.
If int, then draw
max_samples
samples.If float, then draw
max_samples * X.shape[0]
samples.
 max_featuresint or float, optional (default=1.0)
The number of features to draw from X to train each base estimator.
If int, then draw
max_features
features.If float, then draw
max_features * X.shape[1]
features.
 bootstrapboolean, optional (default=True)
Whether samples are drawn with replacement.
 bootstrap_featuresboolean, optional (default=False)
Whether features are drawn with replacement.
 oob_scorebool
Whether to use outofbag samples to estimate the generalization error.
 warm_startbool, optional (default=False)
When set to True, reuse the solution of the previous call to fit and add more estimators to the ensemble, otherwise, just fit a whole new ensemble.
 sampling_strategyfloat, str, dict, callable, (default=’auto’)
Sampling information to sample the data set.
When
float
, it corresponds to the desired ratio of the number of samples in the minority class over the number of samples in the majority class after resampling. Therefore, the ratio is expressed as \alpha_{us} = N_{m} / N_{rM} where N_{m} is the number of samples in the minority class and N_{rM} is the number of samples in the majority class after resampling.Warning
float
is only available for binary classification. An error is raised for multiclass classification.When
str
, specify the class targeted by the resampling. The number of samples in the different classes will be equalized. Possible choices are:'majority'
: resample only the majority class;'not minority'
: resample all classes but the minority class;'not majority'
: resample all classes but the majority class;'all'
: resample all classes;'auto'
: equivalent to'not minority'
.When
dict
, the keys correspond to the targeted classes. The values correspond to the desired number of samples for each targeted class.When callable, function taking
y
and returns adict
. The keys correspond to the targeted classes. The values correspond to the desired number of samples for each class.
 replacementbool, optional (default=False)
Whether or not to sample randomly with replacement or not.
 n_jobsint, optional (default=1)
The number of jobs to run in parallel for both fit and predict. If 1, then the number of jobs is set to the number of cores.
 random_stateint, RandomState instance or None, optional (default=None)
Control the randomization of the algorithm.
If int,
random_state
is the seed used by the random number generator;If
RandomState
instance, random_state is the random number generator;If
None
, the random number generator is theRandomState
instance used bynp.random
.
 verboseint, optional (default=0)
Controls the verbosity of the building process.
 ratiostr, dict, or callable
Deprecated since version 0.4: Use the parameter
sampling_strategy
instead. It will be removed in 0.6.
See also
Notes
This is possible to turn this classifier into a balanced random forest [R5842b76a7f015] by passing a
sklearn.tree.DecisionTreeClassifier
with max_features=’auto’ as a base estimator.See Comparison of ensembling classifiers internally using sampling.
References
 R5842b76a7f011
L. Breiman, “Pasting small votes for classification in large databases and online”, Machine Learning, 36(1), 85103, 1999.
 R5842b76a7f012
L. Breiman, “Bagging predictors”, Machine Learning, 24(2), 123140, 1996.
 R5842b76a7f013
T. Ho, “The random subspace method for constructing decision forests”, Pattern Analysis and Machine Intelligence, 20(8), 832844, 1998.
 R5842b76a7f014
G. Louppe and P. Geurts, “Ensembles on Random Patches”, Machine Learning and Knowledge Discovery in Databases, 346361, 2012.
 R5842b76a7f015
Chen, Chao, Andy Liaw, and Leo Breiman. “Using random forest to learn imbalanced data.” University of California, Berkeley 110, 2004.
Examples
>>> from collections import Counter >>> from sklearn.datasets import make_classification >>> from sklearn.model_selection import train_test_split >>> from sklearn.metrics import confusion_matrix >>> from imblearn.ensemble import BalancedBaggingClassifier >>> X, y = make_classification(n_classes=2, class_sep=2, ... weights=[0.1, 0.9], n_informative=3, n_redundant=1, flip_y=0, ... n_features=20, n_clusters_per_class=1, n_samples=1000, random_state=10) >>> print('Original dataset shape %s' % Counter(y)) Original dataset shape Counter({1: 900, 0: 100}) >>> X_train, X_test, y_train, y_test = train_test_split(X, y, ... random_state=0) >>> bbc = BalancedBaggingClassifier(random_state=42) >>> bbc.fit(X_train, y_train) BalancedBaggingClassifier(...) >>> y_pred = bbc.predict(X_test) >>> print(confusion_matrix(y_test, y_pred)) [[ 23 0] [ 2 225]]
 Attributes
 base_estimator_estimator
The base estimator from which the ensemble is grown.
 estimators_list of estimators
The collection of fitted base estimators.
estimators_samples_
list of arraysThe subset of drawn samples for each base estimator.
 estimators_features_list of arrays
The subset of drawn features for each base estimator.
 classes_array, shape (n_classes,)
The classes labels.
 n_classes_int or list
The number of classes.
 oob_score_float
Score of the training dataset obtained using an outofbag estimate.
 oob_decision_function_ndarray, shape (n_samples, n_classes)
Decision function computed with outofbag estimate on the training set. If n_estimators is small it might be possible that a data point was never left out during the bootstrap. In this case,
oob_decision_function_
might contain NaN.

__init__
(self, base_estimator=None, n_estimators=10, max_samples=1.0, max_features=1.0, bootstrap=True, bootstrap_features=False, oob_score=False, warm_start=False, sampling_strategy='auto', replacement=False, n_jobs=1, random_state=None, verbose=0, ratio=None)[source]¶ Initialize self. See help(type(self)) for accurate signature.

decision_function
(self, X)[source]¶ Average of the decision functions of the base classifiers.
 Parameters
 X{arraylike, sparse matrix} of shape = [n_samples, n_features]
The training input samples. Sparse matrices are accepted only if they are supported by the base estimator.
 Returns
 scorearray, shape = [n_samples, k]
The decision function of the input samples. The columns correspond to the classes in sorted order, as they appear in the attribute
classes_
. Regression and binary classification are special cases withk == 1
, otherwisek==n_classes
.

property
estimators_samples_
¶ The subset of drawn samples for each base estimator.
Returns a dynamically generated list of indices identifying the samples used for fitting each member of the ensemble, i.e., the inbag samples.
Note: the list is recreated at each call to the property in order to reduce the object memory footprint by not storing the sampling data. Thus fetching the property may be slower than expected.

fit
(self, X, y)[source]¶  Build a Bagging ensemble of estimators from the training
set (X, y).
 Parameters
 X{arraylike, sparse matrix}, shape (n_samples, n_features)
The training input samples.
 yarraylike, shape (n_samples,)
The target values.
 Returns
 selfobject
Returns self.

get_params
(self, deep=True)[source]¶ Get parameters for this estimator.
 Parameters
 deepboolean, optional
If True, will return the parameters for this estimator and contained subobjects that are estimators.
 Returns
 paramsmapping of string to any
Parameter names mapped to their values.

predict
(self, X)[source]¶ Predict class for X.
The predicted class of an input sample is computed as the class with the highest mean predicted probability. If base estimators do not implement a
predict_proba
method, then it resorts to voting. Parameters
 X{arraylike, sparse matrix} of shape = [n_samples, n_features]
The training input samples. Sparse matrices are accepted only if they are supported by the base estimator.
 Returns
 yarray of shape = [n_samples]
The predicted classes.

predict_log_proba
(self, X)[source]¶ Predict class logprobabilities for X.
The predicted class logprobabilities of an input sample is computed as the log of the mean predicted class probabilities of the base estimators in the ensemble.
 Parameters
 X{arraylike, sparse matrix} of shape = [n_samples, n_features]
The training input samples. Sparse matrices are accepted only if they are supported by the base estimator.
 Returns
 parray of shape = [n_samples, n_classes]
The class logprobabilities of the input samples. The order of the classes corresponds to that in the attribute classes_.

predict_proba
(self, X)[source]¶ Predict class probabilities for X.
The predicted class probabilities of an input sample is computed as the mean predicted class probabilities of the base estimators in the ensemble. If base estimators do not implement a
predict_proba
method, then it resorts to voting and the predicted class probabilities of an input sample represents the proportion of estimators predicting each class. Parameters
 X{arraylike, sparse matrix} of shape = [n_samples, n_features]
The training input samples. Sparse matrices are accepted only if they are supported by the base estimator.
 Returns
 parray of shape = [n_samples, n_classes]
The class probabilities of the input samples. The order of the classes corresponds to that in the attribute classes_.

score
(self, X, y, sample_weight=None)[source]¶ Returns the mean accuracy on the given test data and labels.
In multilabel classification, this is the subset accuracy which is a harsh metric since you require for each sample that each label set be correctly predicted.
 Parameters
 Xarraylike, shape = (n_samples, n_features)
Test samples.
 yarraylike, shape = (n_samples) or (n_samples, n_outputs)
True labels for X.
 sample_weightarraylike, shape = [n_samples], optional
Sample weights.
 Returns
 scorefloat
Mean accuracy of self.predict(X) wrt. y.

set_params
(self, **params)[source]¶ Set the parameters of this estimator.
The method works on simple estimators as well as on nested objects (such as pipelines). The latter have parameters of the form
<component>__<parameter>
so that it’s possible to update each component of a nested object. Returns
 self