sitc/ml1/util_ds.py

import numpy as np

# Taken from http://chrisstrelioff.ws/sandbox/2015/06/25/decision_trees_in_python_again_cross_validation.html

def get_code(tree, feature_names, target_names,
             spacer_base="    "):
    """Produce psuedo-code for decision tree.

    Args
    ----
    tree -- scikit-leant DescisionTree.
    feature_names -- list of feature names.
    target_names -- list of target (class) names.
    spacer_base -- used for spacing code (default: "    ").

    Notes
    -----
    based on http://stackoverflow.com/a/30104792.
    """
    left      = tree.tree_.children_left
    right     = tree.tree_.children_right
    threshold = tree.tree_.threshold
    features  = [feature_names[i] for i in tree.tree_.feature]
    value = tree.tree_.value

    def recurse(left, right, threshold, features, node, depth):
        spacer = spacer_base * depth
        if (threshold[node] != -2):
            print(spacer + "if ( " + features[node] + " <= " + \
                  str(threshold[node]) + " ) {")
            if left[node] != -1:
                    recurse(left, right, threshold, features,
                            left[node], depth+1)
            print(spacer + "}\n" + spacer +"else {")
            if right[node] != -1:
                    recurse(left, right, threshold, features,
                            right[node], depth+1)
            print(spacer + "}")
        else:
            target = value[node]
            for i, v in zip(np.nonzero(target)[1],
                            target[np.nonzero(target)]):
                target_name = target_names[i]
                target_count = int(v)
                print(spacer + "return " + str(target_name) + \
                      " ( " + str(target_count) + " examples )")

    recurse(left, right, threshold, features, 0, 0)

# Taken from http://scikit-learn.org/stable/auto_examples/tree/plot_iris.html#example-tree-plot-iris-py
import numpy as np
import matplotlib.pyplot as plt

from sklearn.datasets import load_iris
from sklearn.tree import DecisionTreeClassifier

def plot_tree_iris():
    """

    Taken fromhttp://scikit-learn.org/stable/auto_examples/tree/plot_iris.html
    """
    # Parameters
    n_classes = 3
    plot_colors = "bry"
    plot_step = 0.02

    # Load data
    iris = load_iris()

    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

        # Shuffle
        idx = np.arange(X.shape[0])
        np.random.seed(13)
        np.random.shuffle(idx)
        X = X[idx]
        y = y[idx]

        # Standardize
        mean = X.mean(axis=0)
        std = X.std(axis=0)
        X = (X - mean) / std

        # Train
        model = DecisionTreeClassifier(max_depth=3, random_state=1).fit(X, y)

        # Plot the decision boundary
        plt.subplot(2, 3, pairidx + 1)

        x_min, x_max = X[:, 0].min() - 1, X[:, 0].max() + 1
        y_min, y_max = X[:, 1].min() - 1, X[:, 1].max() + 1
        xx, yy = np.meshgrid(np.arange(x_min, x_max, plot_step),
                 np.arange(y_min, y_max, plot_step))

        Z = model.predict(np.c_[xx.ravel(), yy.ravel()])
        Z = Z.reshape(xx.shape)
        cs = plt.contourf(xx, yy, Z, cmap=plt.cm.Paired)

        plt.xlabel(iris.feature_names[pair[0]])
        plt.ylabel(iris.feature_names[pair[1]])
        plt.axis("tight")

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

        plt.axis("tight")

    plt.suptitle("Decision surface of a decision tree using paired features")
    plt.legend()
    plt.show()