knn是最简单的机器学习算法,也是最不需要数学知识的算法。
算法步骤:
import numpy as np from math import sqrt from collections import Counter import matplotlib.pyplot as plt class KNNClassifier: def __init__(self, k): """初始化kNN分类器""" assert k >= 1, "k must be valid" self.k = k self._X_train = None self._y_train = None def fit(self, X_train, y_train): """根据训练数据集X_train和y_train训练kNN分类器""" assert X_train.shape[0] == y_train.shape[0], \ "the size of X_train must be equal to the size of y_train" assert self.k <= X_train.shape[0], \ "the size of X_train must be at least k." self._X_train = X_train self._y_train = y_train return self def predict(self, X_predict): """给定待预测数据集X_predict,返回表示X_predict的结果向量""" assert self._X_train is not None and self._y_train is not None, \ "must fit before predict!" assert X_predict.shape[1] == self._X_train.shape[1], \ "the feature number of X_predict must be equal to X_train" y_predict = [self._predict(x) for x in X_predict] return np.array(y_predict) def _predict(self, x): """给定单个待预测数据x,返回x的预测结果值""" assert x.shape[0] == self._X_train.shape[1], \ "the feature number of x must be equal to X_train" distances = [sqrt(np.sum((x_train - x) ** 2)) for x_train in self._X_train] nearest = np.argsort(distances) topK_y = [self._y_train[i] for i in nearest[:self.k]] votes = Counter(topK_y) return votes.most_common(1)[0][0] def __repr__(self): return "KNN(k=%d)" % self.k raw_data_X = [[3.393533211, 2.331273381], [3.110073483, 1.781539638], [1.343808831, 3.368360954], [3.582294042, 4.679179110], [2.280362439, 2.866990263], [7.423436942, 4.696522875], [5.745051997, 3.533989803], [9.172168622, 2.511101045], [7.792783481, 3.424088941], [7.939820817, 0.791637231] ] raw_data_y = [0, 0, 0, 0, 0, 1, 1, 1, 1, 1] X_train = np.array(raw_data_X) y_train = np.array(raw_data_y) x = np.array([8.093607318, 3.365731514]) X_predict = x.reshape(1, -1) knn_clf = KNNClassifier(3) knn_clf.fit(X_train, y_train) y_predict = knn_clf.predict(X_predict) print(y_predict[0]) plt.scatter(X_train[y_train==0,0],X_train[y_train==0,1]) plt.scatter(X_train[y_train==1,0],X_train[y_train==1,1]) plt.scatter(X_predict[0][0],X_predict[0][1]) plt.show()