sklearn-knn-demo.py

#!/usr/bin/python
# coding:utf8

"""
Created on 2017-06-28
Updated on 2017-06-28
KNN: k近邻算法
Author: 小瑶
GitHub: https://github.com/apachecn/AiLearning
"""
from __future__ import print_function
print(__doc__)

import numpy as np
import matplotlib.pyplot as plt
from numpy import *
from matplotlib.colors import ListedColormap
from sklearn import neighbors, datasets

n_neighbors = 3

# 导入一些要玩的数据
# iris = datasets.load_iris()
# X = iris.data[:, :2]  # 我们只采用前两个feature. 我们可以使用二维数据集避免这个丑陋的切片
# y = iris.target

# print 'X=', type(X), X
# print 'y=', type(y), y

X = array([[-1.0, -1.1], [-1.0, -1.0], [0, 0], [1.0, 1.1], [2.0, 2.0], [2.0, 2.1]])
y = array([0, 0, 0, 1, 1, 1])

# print 'X=', type(X), X
# print 'y=', type(y), y

h = .02  # 网格中的步长

# 创建彩色的地图
# cmap_light = ListedColormap(['#FFAAAA', '#AAFFAA', '#AAAAFF'])
# cmap_bold = ListedColormap(['#FF0000', '#00FF00', '#0000FF'])

cmap_light = ListedColormap(['#FFAAAA', '#AAFFAA'])
cmap_bold = ListedColormap(['#FF0000', '#00FF00'])

for weights in ['uniform', 'distance']:
    # 我们创建了一个knn分类器的实例，并适合数据。
    clf = neighbors.KNeighborsClassifier(n_neighbors, weights=weights)
    clf.fit(X, y)

    # 绘制决策边界。为此，我们将为每个分配一个颜色
    # 来绘制网格中的点 [x_min, x_max]x[y_min, y_max].
    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, h),
                         np.arange(y_min, y_max, h))
    Z = clf.predict(np.c_[xx.ravel(), yy.ravel()])

    # 将结果放入一个彩色图中
    Z = Z.reshape(xx.shape)
    plt.figure()
    plt.pcolormesh(xx, yy, Z, cmap=cmap_light)

    # 绘制训练点
    plt.scatter(X[:, 0], X[:, 1], c=y, cmap=cmap_bold)
    plt.xlim(xx.min(), xx.max())
    plt.ylim(yy.min(), yy.max())
    plt.title("3-Class classification (k = %i, weights = '%s')"
              % (n_neighbors, weights))

plt.show()