wehub-resource-sync
415 lines
12 KiB
Python
415 lines
12 KiB
Python
# Sebastian Raschka, 2015 (http://sebastianraschka.com)
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# Python Machine Learning - Code Examples
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#
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# Chapter 2 - Training Machine Learning Algorithms for Classification
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#
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# S. Raschka. Python Machine Learning. Packt Publishing Ltd., 2015.
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# GitHub Repo: https://github.com/rasbt/python-machine-learning-book
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#
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# License: MIT
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# https://github.com/rasbt/python-machine-learning-book/blob/master/LICENSE.txt
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import numpy as np
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import pandas as pd
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import matplotlib.pyplot as plt
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from matplotlib.colors import ListedColormap
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class Perceptron(object):
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"""Perceptron classifier.
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Parameters
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------------
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eta : float
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Learning rate (between 0.0 and 1.0)
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n_iter : int
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Passes over the training dataset.
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Attributes
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-----------
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w_ : 1d-array
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Weights after fitting.
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errors_ : list
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Number of misclassifications (updates) in each epoch.
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"""
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def __init__(self, eta=0.01, n_iter=10):
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self.eta = eta
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self.n_iter = n_iter
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def fit(self, X, y):
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"""Fit training data.
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Parameters
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----------
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X : {array-like}, shape = [n_samples, n_features]
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Training vectors, where n_samples is the number of samples and
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n_features is the number of features.
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y : array-like, shape = [n_samples]
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Target values.
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Returns
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-------
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self : object
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"""
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self.w_ = np.zeros(1 + X.shape[1])
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self.errors_ = []
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for _ in range(self.n_iter):
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errors = 0
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for xi, target in zip(X, y):
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update = self.eta * (target - self.predict(xi))
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self.w_[1:] += update * xi
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self.w_[0] += update
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errors += int(update != 0.0)
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self.errors_.append(errors)
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return self
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def net_input(self, X):
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"""Calculate net input"""
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return np.dot(X, self.w_[1:]) + self.w_[0]
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def predict(self, X):
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"""Return class label after unit step"""
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return np.where(self.net_input(X) >= 0.0, 1, -1)
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#############################################################################
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print(50 * '=')
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print('Section: Training a perceptron model on the Iris dataset')
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print(50 * '-')
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df = pd.read_csv('https://archive.ics.uci.edu/ml/'
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'machine-learning-databases/iris/iris.data', header=None)
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print(df.tail())
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#############################################################################
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print(50 * '=')
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print('Plotting the Iris data')
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print(50 * '-')
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# select setosa and versicolor
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y = df.iloc[0:100, 4].values
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y = np.where(y == 'Iris-setosa', -1, 1)
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# extract sepal length and petal length
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X = df.iloc[0:100, [0, 2]].values
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# plot data
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plt.scatter(X[:50, 0], X[:50, 1],
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color='red', marker='o', label='setosa')
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plt.scatter(X[50:100, 0], X[50:100, 1],
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color='blue', marker='x', label='versicolor')
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plt.xlabel('sepal length [cm]')
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plt.ylabel('petal length [cm]')
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plt.legend(loc='upper left')
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# plt.tight_layout()
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# plt.savefig('./images/02_06.png', dpi=300)
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plt.show()
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#############################################################################
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print(50 * '=')
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print('Training the perceptron model')
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print(50 * '-')
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ppn = Perceptron(eta=0.1, n_iter=10)
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ppn.fit(X, y)
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plt.plot(range(1, len(ppn.errors_) + 1), ppn.errors_, marker='o')
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plt.xlabel('Epochs')
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plt.ylabel('Number of misclassifications')
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# plt.tight_layout()
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# plt.savefig('./perceptron_1.png', dpi=300)
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plt.show()
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#############################################################################
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print(50 * '=')
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print('A function for plotting decision regions')
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print(50 * '-')
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def plot_decision_regions(X, y, classifier, resolution=0.02):
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# setup marker generator and color map
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markers = ('s', 'x', 'o', '^', 'v')
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colors = ('red', 'blue', 'lightgreen', 'gray', 'cyan')
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cmap = ListedColormap(colors[:len(np.unique(y))])
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# plot the decision surface
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x1_min, x1_max = X[:, 0].min() - 1, X[:, 0].max() + 1
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x2_min, x2_max = X[:, 1].min() - 1, X[:, 1].max() + 1
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xx1, xx2 = np.meshgrid(np.arange(x1_min, x1_max, resolution),
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np.arange(x2_min, x2_max, resolution))
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Z = classifier.predict(np.array([xx1.ravel(), xx2.ravel()]).T)
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Z = Z.reshape(xx1.shape)
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plt.contourf(xx1, xx2, Z, alpha=0.4, cmap=cmap)
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plt.xlim(xx1.min(), xx1.max())
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plt.ylim(xx2.min(), xx2.max())
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# plot class samples
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for idx, cl in enumerate(np.unique(y)):
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plt.scatter(x=X[y == cl, 0], y=X[y == cl, 1],
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alpha=0.8, c=cmap(idx),
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marker=markers[idx], label=cl)
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plot_decision_regions(X, y, classifier=ppn)
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plt.xlabel('sepal length [cm]')
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plt.ylabel('petal length [cm]')
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plt.legend(loc='upper left')
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# plt.tight_layout()
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# plt.savefig('./perceptron_2.png', dpi=300)
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plt.show()
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#############################################################################
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print(50 * '=')
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print('Implementing an adaptive linear neuron in Python')
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print(50 * '-')
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class AdalineGD(object):
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"""ADAptive LInear NEuron classifier.
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Parameters
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------------
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eta : float
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Learning rate (between 0.0 and 1.0)
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n_iter : int
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Passes over the training dataset.
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Attributes
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-----------
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w_ : 1d-array
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Weights after fitting.
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cost_ : list
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Sum-of-squares cost function value in each epoch.
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"""
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def __init__(self, eta=0.01, n_iter=50):
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self.eta = eta
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self.n_iter = n_iter
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def fit(self, X, y):
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""" Fit training data.
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Parameters
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----------
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X : {array-like}, shape = [n_samples, n_features]
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Training vectors, where n_samples is the number of samples and
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n_features is the number of features.
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y : array-like, shape = [n_samples]
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Target values.
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Returns
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-------
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self : object
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"""
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self.w_ = np.zeros(1 + X.shape[1])
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self.cost_ = []
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for i in range(self.n_iter):
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output = self.net_input(X)
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errors = (y - output)
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self.w_[1:] += self.eta * X.T.dot(errors)
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self.w_[0] += self.eta * errors.sum()
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cost = (errors**2).sum() / 2.0
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self.cost_.append(cost)
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return self
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def net_input(self, X):
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"""Calculate net input"""
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return np.dot(X, self.w_[1:]) + self.w_[0]
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def activation(self, X):
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"""Compute linear activation"""
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return self.net_input(X)
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def predict(self, X):
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"""Return class label after unit step"""
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return np.where(self.activation(X) >= 0.0, 1, -1)
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fig, ax = plt.subplots(nrows=1, ncols=2, figsize=(8, 4))
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ada1 = AdalineGD(n_iter=10, eta=0.01).fit(X, y)
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ax[0].plot(range(1, len(ada1.cost_) + 1), np.log10(ada1.cost_), marker='o')
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ax[0].set_xlabel('Epochs')
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ax[0].set_ylabel('log(Sum-squared-error)')
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ax[0].set_title('Adaline - Learning rate 0.01')
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ada2 = AdalineGD(n_iter=10, eta=0.0001).fit(X, y)
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ax[1].plot(range(1, len(ada2.cost_) + 1), ada2.cost_, marker='o')
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ax[1].set_xlabel('Epochs')
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ax[1].set_ylabel('Sum-squared-error')
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ax[1].set_title('Adaline - Learning rate 0.0001')
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# plt.tight_layout()
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# plt.savefig('./adaline_1.png', dpi=300)
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plt.show()
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print('standardize features')
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X_std = np.copy(X)
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X_std[:, 0] = (X[:, 0] - X[:, 0].mean()) / X[:, 0].std()
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X_std[:, 1] = (X[:, 1] - X[:, 1].mean()) / X[:, 1].std()
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ada = AdalineGD(n_iter=15, eta=0.01)
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ada.fit(X_std, y)
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plot_decision_regions(X_std, y, classifier=ada)
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plt.title('Adaline - Gradient Descent')
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plt.xlabel('sepal length [standardized]')
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plt.ylabel('petal length [standardized]')
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plt.legend(loc='upper left')
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# plt.tight_layout()
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# plt.savefig('./adaline_2.png', dpi=300)
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plt.show()
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plt.plot(range(1, len(ada.cost_) + 1), ada.cost_, marker='o')
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plt.xlabel('Epochs')
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plt.ylabel('Sum-squared-error')
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# plt.tight_layout()
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# plt.savefig('./adaline_3.png', dpi=300)
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plt.show()
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#############################################################################
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print(50 * '=')
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print('Large scale machine learning and stochastic gradient descent')
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print(50 * '-')
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class AdalineSGD(object):
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"""ADAptive LInear NEuron classifier.
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Parameters
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------------
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eta : float
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Learning rate (between 0.0 and 1.0)
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n_iter : int
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Passes over the training dataset.
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Attributes
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-----------
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w_ : 1d-array
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Weights after fitting.
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cost_ : list
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Sum-of-squares cost function value averaged over all
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training samples in each epoch.
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shuffle : bool (default: True)
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Shuffles training data every epoch if True to prevent cycles.
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random_state : int (default: None)
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Set random state for shuffling and initializing the weights.
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"""
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def __init__(self, eta=0.01, n_iter=10, shuffle=True, random_state=None):
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self.eta = eta
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self.n_iter = n_iter
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self.w_initialized = False
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self.shuffle = shuffle
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if random_state:
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np.random.seed(random_state)
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def fit(self, X, y):
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""" Fit training data.
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Parameters
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----------
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X : {array-like}, shape = [n_samples, n_features]
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Training vectors, where n_samples is the number of samples and
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n_features is the number of features.
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y : array-like, shape = [n_samples]
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Target values.
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Returns
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-------
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self : object
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"""
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self._initialize_weights(X.shape[1])
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self.cost_ = []
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for i in range(self.n_iter):
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if self.shuffle:
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X, y = self._shuffle(X, y)
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cost = []
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for xi, target in zip(X, y):
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cost.append(self._update_weights(xi, target))
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avg_cost = sum(cost) / len(y)
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self.cost_.append(avg_cost)
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return self
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def partial_fit(self, X, y):
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"""Fit training data without reinitializing the weights"""
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if not self.w_initialized:
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self._initialize_weights(X.shape[1])
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if y.ravel().shape[0] > 1:
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for xi, target in zip(X, y):
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self._update_weights(xi, target)
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else:
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self._update_weights(X, y)
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return self
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def _shuffle(self, X, y):
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"""Shuffle training data"""
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r = np.random.permutation(len(y))
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return X[r], y[r]
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def _initialize_weights(self, m):
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"""Initialize weights to zeros"""
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self.w_ = np.zeros(1 + m)
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self.w_initialized = True
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def _update_weights(self, xi, target):
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"""Apply Adaline learning rule to update the weights"""
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output = self.net_input(xi)
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error = (target - output)
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self.w_[1:] += self.eta * xi.dot(error)
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self.w_[0] += self.eta * error
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cost = 0.5 * error**2
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return cost
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def net_input(self, X):
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"""Calculate net input"""
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return np.dot(X, self.w_[1:]) + self.w_[0]
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def activation(self, X):
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"""Compute linear activation"""
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return self.net_input(X)
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def predict(self, X):
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"""Return class label after unit step"""
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return np.where(self.activation(X) >= 0.0, 1, -1)
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ada = AdalineSGD(n_iter=15, eta=0.01, random_state=1)
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ada.fit(X_std, y)
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plot_decision_regions(X_std, y, classifier=ada)
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plt.title('Adaline - Stochastic Gradient Descent')
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plt.xlabel('sepal length [standardized]')
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plt.ylabel('petal length [standardized]')
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plt.legend(loc='upper left')
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# plt.tight_layout()
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# plt.savefig('./adaline_4.png', dpi=300)
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plt.show()
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plt.plot(range(1, len(ada.cost_) + 1), ada.cost_, marker='o')
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plt.xlabel('Epochs')
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plt.ylabel('Average Cost')
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# plt.tight_layout()
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# plt.savefig('./adaline_5.png', dpi=300)
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plt.show()
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ada = ada.partial_fit(X_std[0, :], y[0])
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