Class Balance

Oftentimes classifiers perform badly because of a class imbalance. A class balance chart can help prepare the user for such a case by showing the support for each class in the fitted classification model.

# Load the classification data set
data = load_data('occupancy')

# Specify the features of interest and the classes of the target
features = ["temperature", "relative humidity", "light", "C02", "humidity"]
classes = ['unoccupied', 'occupied']

# Extract the numpy arrays from the data frame
X = data[features].as_matrix()
y = data.occupancy.as_matrix()

# Create the train and test data
X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.2)
# Instantiate the classification model and visualizer
forest = RandomForestClassifier()
visualizer = ClassBalance(forest, classes=classes), y_train)  # Fit the training data to the visualizer
visualizer.score(X_test, y_test)  # Evaluate the model on the test data
g = visualizer.poof()             # Draw/show/poof the data

API Reference

Class balance visualizer for showing per-class support.

class yellowbrick.classifier.class_balance.ClassBalance(model, ax=None, classes=None, **kwargs)[source]

Bases: yellowbrick.classifier.base.ClassificationScoreVisualizer

Class balance chart that shows the support for each class in the fitted classification model displayed as a bar plot. It is initialized with a fitted model and generates a class balance chart on draw.


ax: axes

the axis to plot the figure on.

model: estimator

Scikit-Learn estimator object. Should be an instance of a classifier, else __init__() will raise an exception.

classes: list

A list of class names for the legend. If classes is None and a y value is passed to fit then the classes are selected from the target vector.

kwargs: dict

Keyword arguments passed to the super class. Here, used to colorize the bars in the histogram.


These parameters can be influenced later on in the visualization process, but can and should be set as early as possible.


Renders the class balance chart across the axis.

Returns:ax : the axis with the plotted figure

Finalize executes any subclass-specific axes finalization steps. The user calls poof and poof calls finalize.

Parameters:kwargs: generic keyword arguments.
score(X, y=None, **kwargs)[source]

Generates the Scikit-Learn precision_recall_fscore_support


X : ndarray or DataFrame of shape n x m

A matrix of n instances with m features

y : ndarray or Series of length n

An array or series of target or class values


ax : the axis with the plotted figure