Plot the decision boundaries of a VotingClassifier#

Plot the decision boundaries of a VotingClassifier for two features of the Iris dataset.

Plot the class probabilities of the first sample in a toy dataset predicted by three different classifiers and averaged by the VotingClassifier.

First, three exemplary classifiers are initialized (DecisionTreeClassifier, KNeighborsClassifier, and SVC) and used to initialize a soft-voting VotingClassifier with weights [2, 1, 2], which means that the predicted probabilities of the DecisionTreeClassifier and SVC each count 2 times as much as the weights of the KNeighborsClassifier classifier when the averaged probability is calculated.

Decision Tree (depth=4), KNN (k=7), Kernel SVM, Soft Voting

from itertools import product

import matplotlib.pyplot as plt

from sklearn import datasets
from sklearn.ensemble import VotingClassifier
from sklearn.inspection import DecisionBoundaryDisplay
from sklearn.neighbors import KNeighborsClassifier
from sklearn.svm import SVC
from sklearn.tree import DecisionTreeClassifier

# Loading some example data
iris = datasets.load_iris()
X = iris.data[:, [0, 2]]
y = iris.target

# Training classifiers
clf1 = DecisionTreeClassifier(max_depth=4)
clf2 = KNeighborsClassifier(n_neighbors=7)
clf3 = SVC(gamma=0.1, kernel="rbf", probability=True)
eclf = VotingClassifier(
    estimators=[("dt", clf1), ("knn", clf2), ("svc", clf3)],
    voting="soft",
    weights=[2, 1, 2],
)

clf1.fit(X, y)
clf2.fit(X, y)
clf3.fit(X, y)
eclf.fit(X, y)

# Plotting decision regions
f, axarr = plt.subplots(2, 2, sharex="col", sharey="row", figsize=(10, 8))
for idx, clf, tt in zip(
    product([0, 1], [0, 1]),
    [clf1, clf2, clf3, eclf],
    ["Decision Tree (depth=4)", "KNN (k=7)", "Kernel SVM", "Soft Voting"],
):
    DecisionBoundaryDisplay.from_estimator(
        clf, X, alpha=0.4, ax=axarr[idx[0], idx[1]], response_method="predict"
    )
    axarr[idx[0], idx[1]].scatter(X[:, 0], X[:, 1], c=y, s=20, edgecolor="k")
    axarr[idx[0], idx[1]].set_title(tt)

plt.show()