Plot the decision surface of decision trees trained on the iris dataset

Plot the decision surface of a decision tree and oblique decision tree trained on pairs of features of the iris dataset.

See decision tree for more information on the estimators.

For each pair of iris features, the decision tree learns axis-aligned decision boundaries made of combinations of simple thresholding rules inferred from the training samples. The oblique decision tree learns oblique decision boundaries made from linear combinations of the features in the training samples and then the same thresholding rule as regular decision trees.

We also show the tree structure of a model built on all of the features.

import matplotlib.pyplot as plt
import numpy as np
from sklearn.datasets import load_iris
from sklearn.inspection import DecisionBoundaryDisplay

from treeple._lib.sklearn.tree import DecisionTreeClassifier, plot_tree
from treeple.tree import ObliqueDecisionTreeClassifier

First load the copy of the Iris dataset shipped with scikit-learn:

iris = load_iris()

# Parameters
n_classes = 3
plot_colors = "ryb"
plot_step = 0.02

clf_labels = ["Axis-aligned", "Oblique"]
random_state = 123456

clfs = [
    DecisionTreeClassifier(random_state=random_state),
    ObliqueDecisionTreeClassifier(random_state=random_state),
]

for clf, clf_label in zip(clfs, clf_labels):
    fig, axes = plt.subplots(2, 3)
    axes = axes.flatten()

    for pairidx, pair in enumerate([[0, 1], [0, 2], [0, 3], [1, 2], [1, 3], [2, 3]]):
        # We only take the two corresponding features
        X = iris.data[:, pair]
        y = iris.target

        # Train
        clf.fit(X, y)

        # Plot the decision boundary
        ax = axes[pairidx]
        plt.tight_layout(h_pad=0.5, w_pad=0.5, pad=2.5)
        DecisionBoundaryDisplay.from_estimator(
            clf,
            X,
            cmap=plt.cm.RdYlBu,
            response_method="predict",
            ax=ax,
            xlabel=iris.feature_names[pair[0]],
            ylabel=iris.feature_names[pair[1]],
        )

        # Plot the training points
        for i, color in zip(range(n_classes), plot_colors):
            idx = np.where(y == i)
            ax.scatter(
                X[idx, 0],
                X[idx, 1],
                c=color,
                label=iris.target_names[i],
                cmap=plt.cm.RdYlBu,
                edgecolor="black",
                s=15,
            )

    fig.suptitle(f"Decision surface of {clf_label} decision trees trained on pairs of features")
    plt.legend(loc="lower right", borderpad=0, handletextpad=0)
    _ = plt.axis("tight")
    plt.show()

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/home/circleci/project/examples/sklearn_vs_treeple/plot_iris_dtc.py:73: UserWarning: No data for colormapping provided via 'c'. Parameters 'cmap' will be ignored
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  ax.scatter(

Display the structure of a single decision tree trained on all the features together.

for clf, clf_label in zip(clfs, clf_labels):
    plt.figure()
    clf.fit(iris.data, iris.target)
    plot_tree(clf, filled=True)
    plt.title(f"{clf_label} decision tree trained on all the iris features")
    plt.show()

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Estimated memory usage: 225 MB