ch7-AdaBoost.py

import pandas as pd
df_wine = pd.read_csv('https://archive.ics.uci.edu/ml/machine-learning-databases/wine/wine.data', header=None)
df_wine.columns = ['Class label', 'Alcohol',
                    'Malic acid', 'Ash',
                    'Alcalinity of ash',
                    'Magnesium', 'Total phenols',
                    'Flavanoids', 'Nonflavanoid phenols',
                    'Proanthocyanins',
                    'Color intensity', 'Hue',
                    'OD280/OD315 of diluted wines',
                    'Proline']

df_wine = df_wine[df_wine['Class label'] != 1]
y = df_wine['Class label'].values
X = df_wine[['Alcohol', 'Hue']].values

from sklearn.preprocessing import LabelEncoder
from sklearn.cross_validation import train_test_split
le = LabelEncoder()
y = le.fit_transform(y)
X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.40, random_state=1)


from sklearn.ensemble import AdaBoostClassifier
from sklearn.tree import DecisionTreeClassifier
from sklearn.metrics import accuracy_score
tree = DecisionTreeClassifier(criterion='entropy',
                               max_depth=None,
                               random_state=0)

ada = AdaBoostClassifier(base_estimator=tree,
                          n_estimators=500,
                          learning_rate=0.1,
                          random_state=0)

tree = tree.fit(X_train, y_train)
y_train_pred = tree.predict(X_train)
y_test_pred = tree.predict(X_test)
tree_train = accuracy_score(y_train, y_train_pred)
tree_test = accuracy_score(y_test, y_test_pred)
print('Decision tree train/test accuracies %.3f/%.3f'% (tree_train, tree_test))

ada = ada.fit(X_train, y_train)
y_train_pred = ada.predict(X_train)
y_test_pred = ada.predict(X_test)
ada_train = accuracy_score(y_train, y_train_pred)
ada_test = accuracy_score(y_test, y_test_pred)
print('AdaBoost train/test accuracies %.3f/%.3f' % (ada_train, ada_test))



# Plot
import numpy as np
import matplotlib.pyplot as plt

x_min = X_train[:, 0].min() - 1
x_max = X_train[:, 0].max() + 1
y_min = X_train[:, 1].min() - 1
y_max = X_train[:, 1].max() + 1
xx, yy = np.meshgrid(np.arange(x_min, x_max, 0.1), np.arange(y_min, y_max, 0.1))
f, axarr = plt.subplots(1, 2, sharex='col', sharey='row', figsize=(8, 3))

for idx, clf, tt in zip([0, 1], [tree, ada], ['Decision Tree', 'AdaBoost']):
    clf.fit(X_train, y_train)
    Z = clf.predict(np.c_[xx.ravel(), yy.ravel()])
    Z = Z.reshape(xx.shape)
    axarr[idx].contourf(xx, yy, Z, alpha=0.3)
    axarr[idx].scatter(X_train[y_train==0, 0],
                        X_train[y_train==0, 1],
                        c='blue',
                        marker='^')
    axarr[idx].scatter(X_train[y_train==1, 0],
                        X_train[y_train==1, 1],
                        c='red',
                        marker='o')
    axarr[idx].set_title(tt)
    axarr[0].set_ylabel('Alcohol', fontsize=12)


plt.text(10.2, -1.2,
          s='Hue',
          ha='center',
          va='center',
          fontsize=12)
plt.show()