How to use the VotingClassifier in scikit-learn.

Using the VotingClassifier

To run the code yourself, you'll need to make sure the following tools are loaded.

import numpy as np
import matplotlib.pylab as plt
from sklearn.tree import DecisionTreeClassifier
from sklearn.linear_model import LogisticRegression
from sklearn.neighbors import KNeighborsClassifier
from sklearn.ensemble import VotingClassifier
from sklearn.datasets import make_classification

The classification problem that we'll try to solve is generated.

X, y = make_classification(n_samples=2000, n_features=2,
                           n_redundant=0, random_state=21,
                           class_sep=1.75, flip_y=0.1)
plt.scatter(X[:, 0], X[:, 1], c=y, s=5);

To get the pretty plots you'll need the following function.

def make_plots():
    X_new = np.concatenate([
        np.random.uniform(np.min(X[:, 0]), np.max(X[:, 0]), (20000, 1)),
        np.random.uniform(np.min(X[:, 1]), np.max(X[:, 1]), (20000, 1))
    ], axis=1)
    plt.figure(figsize=(16, 4))
    plt.subplot(141)
    plt.scatter(X[:, 0], X[:, 1], c=y, s=5)
    plt.title("original data")
    plt.subplot(142)
    plt.scatter(X_new[:, 0], X_new[:, 1], c=clf1.predict_proba(X_new)[:, 1], s=5)
    plt.title("ens1")
    plt.subplot(143)
    plt.scatter(X_new[:, 0], X_new[:, 1], c=clf2.predict_proba(X_new)[:, 1], s=5)
    plt.title("ens2")
    plt.subplot(144)
    plt.scatter(X_new[:, 0], X_new[:, 1], c=clf3.predict_proba(X_new)[:, 1], s=5)
    plt.title("ens3");

To train the three models and get the visuals you can run:

clf1 = LogisticRegression().fit(X, y)
clf2 = KNeighborsClassifier(n_neighbors=10).fit(X, y)
clf3 = VotingClassifier(estimators=[('clf1', clf1), ('clf2', clf2)],
                        voting='soft',
                        weights=[10.5, 2.5])
clf3.fit(X, y)

make_plots()

Make sure you play with the weights parameter to get a feel of the effect.