鸢尾花数据集的KNN探索与乳腺癌决策树洞察

鸢尾花数据集的KNN探索与乳腺癌决策树洞察

今天博主做了这个KNN和决策树的实验。

一.数据集介绍

介绍一下数据集：

威斯康星州乳腺癌数据集：

威斯康星州乳腺癌数据集（Wisconsin Breast Cancer Dataset）是一个经典的机器学习数据集，它最初由威斯康星州医院的Dr. William H. Wolberg收集。这个数据集被广泛用于分类任务、特征选择、模型评估等机器学习任务和实验中 数据类型：这是一份多变量数据集，包含了乳腺癌的生理参数。
数据集特征：
特征：数据集由 30 个特征组成，这些特征是图像分析得到的，包括纹理、面积、平滑度、凸性、颗粒度等统计参数。
目标变量：数据集的目标变量是二分类的，即是否患有乳腺癌，用 0 和 1 表示。
样本数量：数据集包含 569 个样本。

鸢尾花数据集

鸢尾花数据集最初由Edgar Anderson测量得到，而后在著名的统计学家和生物学家R.A Fisher于1936年发表的文章中被引入到统计和机器学习领域数据集特征：
鸢尾花数据集包含了150个样本，每个样本有4个特征，这些特征是从花朵的尺寸测量中得到的，具体包括：
花萼长度（sepal length）：在厘米单位下的花朵萼片的长度。
花萼宽度（sepal width）：花萼片的宽度。
花瓣长度（petal length）：花瓣的长度。
花瓣宽度（petal width）：花瓣的宽度。

看一下我们的代码：

决策树代码：

from sklearn.datasets import load_breast_cancer
import matplotlib.pyplot as plt
import pandas as pd
breast_cancer=load_breast_cancer()
from sklearn.tree import plot_tree
#df = pd.DataFrame(breast_cancer.target, columns=breast_cancer.feature_names)
#df.to_csv(r'D:\coursework\maching_learning\breast_cancer.csv', index=None)
#print(type(breast_cancer))

#df = pd.DataFrame(breast_cancer.target, columns="label")
#df.to_csv(r'D:\coursework\maching_learning\breast_cancer_label.csv', index=None)
#print(type(breast_cancer))

print('breast_cancer数据集特征')
print(breast_cancer.data[:5])
print('breast_cancer数据集标签')
print(breast_cancer.target[:5])


#2.进行数据集分割。

from sklearn.model_selection import train_test_split
data_train,data_test,target_train,target_test=train_test_split(breast_cancer.data,breast_cancer.target,test_size=0.2)


#3.配置决策树模型。
from sklearn import tree # 导入决策树包
clf = tree.DecisionTreeClassifier() #加载决策树模型
#4.训练决策树模型。
clf.fit(data_train, target_train)

#5.模型预测。
predictions = clf.predict(data_test) # 模型测试
predictions[:10]
#6.模型评估。
from sklearn.metrics import accuracy_score # 导入准确率评价指标
print('Accuracy:%s'% accuracy_score(target_test, predictions))

#7.参数调优。可以根据评估结果，对模型设置或调整为更优的参数，使评估结果更准确。
#信息增益--entropy
criterions=['gini','entropy']
for  ct in criterions:

    clf2 = tree.DecisionTreeClassifier(criterion =  ct)
    clf2.fit(data_train, target_train)

    plot_tree(clf2,filled=True, class_names=breast_cancer.target_names,label=ct)
    predictions2 = clf2.predict(data_test) # 模型测试
 #   print('第一种：采用信息增益后的Accuracy:%s'% accuracy_score(target_test, predictions2))
    #最大深度--max_depth
    import numpy as np
    max_depths = np.linspace(1, 32, 32, endpoint=True)
    scores=[]
    for i in max_depths:
        clf3 = tree.DecisionTreeClassifier(max_depth=i)
        clf3.fit(data_train, target_train)
        predictions3 = clf3.predict(data_test) # 模型测试
        scores.append(accuracy_score(target_test,predictions3))
    import matplotlib.pyplot as plt
    plt.figure()
    plt.plot(scores)
    plt.title('max_depth-accuracy_score,'+"criterion = "+ct)
    plt.xlabel('max_depth')
    plt.ylabel('accuracy_score')
 
    plt.show()
    max_score_index=np.argmax(scores)+1
    print('可见当max-depth=',max_score_index,'时为最优其准确率为:',scores[max_score_index-1])

后剪枝与预剪枝代码：

import math
import pandas as pd
import matplotlib.pyplot as plt
# 设置中文显示字体
from pylab import mpl
import copy
mpl.rcParams["font.sans-serif"] = ["SimHei"]

# 使用文本注释绘制树节点
decision_node = dict(boxstyle='sawtooth', fc='0.8')
leaf_node = dict(boxstyle='round4', fc='0.8')
arrow_args = dict(arrowstyle='<-')

# 节点
def plotNode(nodeTxt, centerPt, parentPt, nodeType):
    createPlot.ax1.annotate(nodeTxt, xy=parentPt, xycoords='axes fraction',
                            xytext=centerPt, textcoords='axes fraction',
                            va="center", ha="center", bbox=nodeType, arrowprops=arrow_args)

# 获取叶节点的数目
def getNumLeafs(my_tree):
    num_leafs = 0
    first_str = list(my_tree.keys())[0]
    second_dict = my_tree[first_str]
    for key in second_dict.keys():
        if type(second_dict[key]).__name__ == 'dict':
            num_leafs += getNumLeafs(second_dict[key])
        else:
            num_leafs += 1
    return num_leafs

# 获取树的深度
def getTreeDepth(my_tree):
    max_depth = 0
    first_str = list(my_tree.keys())[0]
    second_dict = my_tree[first_str]
    for key in second_dict.keys():
        if type(second_dict[key]).__name__ == 'dict':
            this_depth = 1 + getTreeDepth(second_dict[key])
        else:
            this_depth = 1
        if this_depth > max_depth:
            max_depth = this_depth
    return max_depth

# 绘制树中文本
def plotMidText(cntr_pt, parent_pt, txt_string):
    x_mid = (parent_pt[0] - cntr_pt[0]) / 2.0 + cntr_pt[0]
    y_mid = (parent_pt[1] - cntr_pt[1]) / 2.0 + cntr_pt[1]
    createPlot.ax1.text(x_mid, y_mid, txt_string)

# 绘制树
def plotTree(my_tree, parent_pt, node_txt):
    num_leafs = getNumLeafs(my_tree)
    depth = getTreeDepth(my_tree)
    first_str = list(my_tree.keys())[0]
    cntr_pt = (plotTree.x_off + (1.0 + float(num_leafs)) / 2.0 /plotTree.total_w, plotTree.y_off)

    plotMidText(cntr_pt, parent_pt, node_txt)
    plotNode(first_str, cntr_pt, parent_pt, decision_node)
    second_dict = my_tree[first_str]
    plotTree.y_off = plotTree.y_off - 1.0 / plotTree.total_d
    for key in second_dict.keys():
        if type(second_dict[key]).__name__ == 'dict':
            plotTree(second_dict[key], cntr_pt, str(key))
        else:
            plotTree.x_off = plotTree.x_off + 1.0 / plotTree.total_w
            plotNode(second_dict[key], (plotTree.x_off, plotTree.y_off), cntr_pt, leaf_node)
            plotMidText((plotTree.x_off, plotTree.y_off), cntr_pt, str(key))
    plotTree.y_off = plotTree.y_off + 1.0 / plotTree.total_d

def createPlot(in_tree,method):
    # 新建一个窗口
    fig = plt.figure(1, facecolor='white')
    # 清除图形
    fig.clf()
    axprops = dict(xticks=[], yticks=[])
    # 创建子图
    createPlot.ax1 = plt.subplot(111, frameon=False, **axprops)
    # w为决策树叶子个数
    plotTree.total_w = float(getNumLeafs(in_tree))
    # d为决策树深度
    plotTree.total_d = float(getTreeDepth(in_tree))
    plotTree.x_off = -0.5 / plotTree.total_w
    plotTree.y_off = 1.0
    plotTree(in_tree, (0.5, 1.0), '')
    # 显示
    try:
       plt.title("method="+method,pad=15)
    except:
         plt.title("method=None",pad=15)
    plt.show()
    
def readDataset():   
    '''
    读取csv格式的数据集，返回dataset与labels的list形式
    ''' 
    
    #数据集内有中文字符，读取csv文件时需要使用gbk方式读取
    df = pd.read_csv('data.csv',encoding="utf8")
    #前14个样本作为训练集，后4个样本作为验证集
    trainDf = df.loc[0:350]
    testDf = df.loc[350:]
    #labels为该df的列
    labels = df.columns.tolist()
    #训练集以及测试集为对应df的值
    trainDataset = trainDf.values.tolist()
    testDataset = testDf.values.tolist()
    return trainDataset, testDataset, labels


def Entropy(dataset):
    '''
    计算信息熵并返回
    '''
    
    # 样本个数
    numExamples = len(dataset)
    # 类别计数器
    classCount = {}
    
    # 每个样本的最后一列为刚样本所属的类别，循环每个样本，以每个类别为key，对应的value
    # 就是该类别拥有的样本数
    for example in dataset:
        # example[-1]就为样本的类别
        # 如果类别对应的key不存在就创建对应的key，样本数（value）置0
        if example[-1] not in classCount.keys():
            classCount[example[-1]] = 0   
        # 将类别计数器当中的对应类别的样本数（value） + 1
        classCount[example[-1]] += 1      
    
    # 熵的计算公式为： entropy = pi * log2（pi）
    entropy = 0.0 
    for num in classCount.values():
        # 样本出现概率 = 样本出现次数 / 样本总数
        p = num / numExamples
        entropy -= p * math.log(p,2)
    return entropy

def majorityCnt(classList):   
    '''
    统计每个类别的个数，返回出现次数多的类别
    '''
    
    # 类别计数器
    classCount={}
    for c in classList:
        if c not in classCount.keys():
            classCount[c] = 0
        classCount[c] += 1
    # reverse = True 从大到小排列，key x[1]指比较key、value中的value
    sortedClassCount = sorted(classCount.items(),key=lambda x:x[1],reverse=True)
    return sortedClassCount[0][0]

def splitDataset(dataset, index, splitValue):
    '''
    划分数据集
    index : 该特征的索引
    splitValue : 每次取第i个样本与第i+1个样本的第index个特征的平均值splitValue
    作为数据集划分点,返回子集1与子集2
    '''
    subDataset1 = []
    subDataset2 = []
    # 遍历每个样本，当样本中的第index列的值<splitValue时，归为子集1
    # 当样本中的第index列的值>splitValue时，归为子集2
    for example in dataset:
        if example[index] <= splitValue:
            # 取出分裂特征前的数据集
            splitFeature = example[:index]         
            # 取出分裂特征后的数据集,并合并
            splitFeature.extend(example[index+1:]) 
            # 本行取得的去除example中index列的列表，加入总列表
            subDataset1.append(splitFeature)   
        else:
            # 取出分裂特征前的数据集
            splitFeature = example[:index]         
            # 取出分裂特征后的数据集,并合并
            splitFeature.extend(example[index+1:]) 
            # 本行取得的去除example中index列的列表，加入总列表
            subDataset2.append(splitFeature)   
    return subDataset1, subDataset2

def chooseBestFeatureToSplit(dataset):
    '''
    返回最优特征索引和最佳划分点值
    '''
    
    # 特征数，由于最后一列是类别不是特征，将最后一列去掉
    numFeatures = len(dataset[0]) - 1 
    # 计算原始信息熵
    baseEntropy = Entropy(dataset) 
    # 信息增益
    bestInfoGain = 0 
    # 最优特征下标
    bestIndex = -1     
    # 最佳划分点
    bestSplitValue = 0
    for column in range(0, numFeatures):
        # 取出第i列特征值
        featureList = [example[column] for example in dataset]
        # 排序
        featureList = sorted(featureList)
        
        # 使用第column列特征值的第row行和第row+1行的平均值作为划分点，进行划分
        # 得到左右两个子集
        for row in range(0,len(featureList)-1):   
            newEntropy = 0
            splitValue = (featureList[row] + featureList[row + 1]) / 2.0  
            subDataset1, subDataset2 = splitDataset(dataset,column,splitValue)
            # 权重 = 子集样本数 / 全集样本数
            weight1 = len(subDataset1) / float(len(dataset))
            weight2 = len(subDataset2) / float(len(dataset))
            # 按某个特征分类后的熵 = （子集的熵 * 子集占全集的比重） 的总和
            newEntropy += weight1 * Entropy(subDataset1)  
            newEntropy += weight2 * Entropy(subDataset2)
            # 信息增益 = 原始熵 - 按某个特征分类后的熵
            infoGain = baseEntropy - newEntropy
            # 更新信息增益与对应最佳特征的索引
            if infoGain > bestInfoGain: 
                bestInfoGain = infoGain
                bestIndex = column
                bestSplitValue = splitValue
    return bestIndex, bestSplitValue





def createTree(trainDataset, testDataset, labels, method = None):
    '''
    method 为 [None, 'pre', 'post']中的一种
    None为不使用剪枝操作，
    'pre'为使用预剪枝操作，
    'post'为使用后剪枝操作，
    
    递归建树
    1.获取最佳特征索引bestIndex以及最佳划分点bestSplitValue
    2.根据bestIndex和bestSplitValue将训练集与测试集划分为左右两个子集subDataset1和subDataset2
    3.如选择预剪枝，则每次衡量划分子集前的精确度和划分子集后的精确度，如有提高才生成子树；
    4.如选择后剪枝，则先生成子树，再衡量去除每个子树是否带来精确度的提高，如有提高则去除子树；
    
    返回值：
    1.method为None或'pre'时，返回myTree
    2.method为'post'时，返回myTree与correct
    
    注意：
    这个correct是指由训练集划分出的子树对测试集进行预测，一共预测对多少个样本的个数。
    
    '''
    # 获取训练集与测试集当中的所有类别
    trainClassList = [example[-1] for example in trainDataset] 
    testClassList = [example[-1] for example in testDataset]
    #print(trainClassList)
    # 若训练集中只有一个类时，有两种情况：
    # 1.如果当前采用后剪枝，则返回predict_class与correct
    # 2.如果不剪枝或采用预剪枝，则返回predict_class
    if trainClassList.count(trainClassList[0]) == len(trainClassList):
        
        # 当前子树预测类别
        predict_class = trainClassList[0]
        # 当前预测类别预测测试集对的个数
        correct = testClassList.count(predict_class)
        
        if method == 'post':
            return predict_class, correct
        else: 
            return predict_class
        
    # 若训练集最后只剩下类别，有两种情况：
    # 1.如果当前采用后剪枝，则返回predict_class与correct
    # 2.如果不剪枝或采用预剪枝，则返回predict_class
    if len(trainDataset[0]) == 1: 
        
        # 当前子树预测类别
        predict_class = majorityCnt(trainClassList)
        # 当前预测类别预测测试集对的个数
        correct = testClassList.count(predict_class)
        
        if method == 'post':
            return predict_class, correct
        else: 
            return predict_class
        
    # 找到当前情况下使训练集信息增益最大的特征的索引，以及最佳的划分点值
    bestIndex, bestSplitValue = chooseBestFeatureToSplit(trainDataset) 
   # print(bestIndex)
    print(labels[bestIndex])
    # 最优特征的名字
    bestFeature = labels[bestIndex]
    # 创建决策树 
    myTree = {bestFeature:{}}
    # 从labels中删除最优特征
    #del(labels[bestIndex])
    
    # 使用最优特征索引与最佳参数划分出训练集与测试集的两个子集
    trainSubDataset1, trainSubDataset2 = splitDataset(trainDataset,bestIndex
                                                      ,bestSplitValue)
    testSubDataset1, testSubDataset2 = splitDataset(testDataset,bestIndex
                                                    ,bestSplitValue)
    # 获取训练集与测试集中子集1与子集2的所有类别
    trainSubClassList1 = [example[-1] for example in trainSubDataset1] 
    trainSubClassList2 = [example[-1] for example in trainSubDataset2] 
    testSubClassList1 = [example[-1] for example in testSubDataset1] 
    testSubClassList2 = [example[-1] for example in testSubDataset2] 
    if method == 'pre':
        
        # 划分子集前：
        # 预测类别为当前训练集中最多的类别
        predict_class_pre = majorityCnt(trainClassList)
        # 使用训练集中最多的类别预测当前未划分的测试集的准确度
        precision_pre = testClassList.count(predict_class_pre)/len(testClassList)
        
        # 划分子集后：
        # 子集1的预测类别为当前训练子集1中最多的类别，子集2同理
        predict_class_post1 = majorityCnt(trainSubClassList1)
        predict_class_post2 = majorityCnt(trainSubClassList2)
        # 使用这两个类别分别预测测试集的子集1与子集2的正确总数
        correct1 = testSubClassList1.count(predict_class_post1)
        correct2 = testSubClassList2.count(predict_class_post2)
        totalCorrect = correct1 + correct2
        # 划分子集后的准确率
        precision_post = totalCorrect / len(testClassList)
        print("precision_post",precision_post)

        print("precision_pre",precision_pre)
        # 如果划分子集后的准确率比划分前更高，则划分子集，否则返回当前样本中最多的类别
        if precision_post > precision_pre:
            myTree[bestFeature]["<="+str(bestSplitValue)] = createTree(trainSubDataset1,testSubDataset1, labels, method = 'pre')
            myTree[bestFeature][">"+str(bestSplitValue)] = createTree(trainSubDataset2,testSubDataset2, labels, method = 'pre')
        else:
            return predict_class_pre
    elif method == 'post':
        
        # 剪枝前：
        predict_class_pre = majorityCnt(trainClassList)

        # 生成leftTree与rightTree并得到该子树预测测试集对的数量correct1与correct2
        leftTree, correct1 = createTree(trainSubDataset1,testSubDataset1, labels, 
                                        method = 'post')
        rightTree, correct2 = createTree(trainSubDataset2,testSubDataset2, labels, 
                                         method = 'post')
        totalCorrect = correct1 + correct2
        # 剪枝前的准确率
        if len(testClassList)==0:
            precision_pre=0
        else:
           precision_pre = totalCorrect / len(testClassList)
        
        # 剪枝后
        # 预测类别为当前训练集中最多的类别
        predict_class_post = majorityCnt(trainClassList)
       
        if len(testClassList)==0:
            precision_post=0
        else:
                precision_post = testClassList.count(predict_class_post)/len(testClassList)        # 使用训练集中最多的类别预测剪枝后的测试集的准确度
       
        print(precision_post)
        
        # 如果剪枝后的精确度比剪枝前更高，则进行剪枝，
        # 返回剪枝后的预测类别predict_class_post与剪枝后预测对的个数correct_post；
        # 否则返回剪枝前的树myTree以及剪枝前预测正确的个数totalCorrect
        print("precision_post",precision_post)
        print("precision",precision_pre)
        if precision_post > precision_pre:
            correct_post = testClassList.count(predict_class_pre)
            return predict_class_pre, correct_post
        else:
            myTree[bestFeature]["<="+str(round(bestSplitValue,2))] = leftTree
            myTree[bestFeature][">"+str(round(bestSplitValue,2))] = rightTree
            return myTree, totalCorrect
            
    else :

        myTree[bestFeature]["<="+str(round(bestSplitValue,2))] = createTree(trainSubDataset1,testSubDataset1, labels, method = None)
        myTree[bestFeature][">"+str(round(bestSplitValue,2))] = createTree(trainSubDataset2,testSubDataset2, labels, method = None)
        predict_class_pre = majorityCnt(trainClassList)
        # 使用训练集中最多的类别预测当前未划分的测试集的准确度
        precision_pre = testClassList.count(predict_class_pre)/len(testClassList)
        print("precision",precision_pre)
    return myTree
    
    
    
    
if __name__=='__main__':
    trainDataset, testDataset, labels = readDataset()
    print(labels)
    labelsForPost = copy.deepcopy(labels)
    values = createTree(trainDataset, testDataset, labels, method = "post")
    print(values)
    if len(values) == 1:
        myTree = values 
    elif len(values) == 2:
        myTree = values[0]
    createPlot(myTree, method = "post")

3.KNN+PCA可视化

import numpy as np
from sklearn.datasets import load_iris
from sklearn.model_selection import train_test_split
from sklearn.neighbors import KNeighborsClassifier
from sklearn.metrics import accuracy_score
from sklearn.decomposition import PCA # PCA主成分分析类
import matplotlib.pyplot as plt  # 画图工具
import pandas as pd

# 加载鸢尾花数据集
iris = load_iris()
X = iris.data  # 特征向量
y = iris.target  # 类别标签
#df = pd.DataFrame(iris.data, columns=iris.feature_names)
#df.to_csv(r'D:\coursework\maching_learning\iris.csv', index=None)


 
# 划分训练集和测试集
X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.4, random_state=42)  #训练集占比为0.4
 
# 构建KNN分类器
knn = KNeighborsClassifier(n_neighbors=10)  # 设置邻居数量为10
knn.fit(X_train, y_train)  # 在训练集上训练模型
 
# 在测试集上进行预测
y_pred = knn.predict(X_test)
 
# 计算分类准确率
accuracy = accuracy_score(y_test, y_pred)
print("测试集准确率为: {:.2%}".format(accuracy))





iris = load_iris()
y = iris.target
X = iris.data
#X.shape
#调用PCA
pca = PCA(n_components=2) # 降到2维
pca = pca.fit(X) #拟合模型
X_dr = pca.transform(X) #获取新矩阵 （降维后的）
#X_dr



#也可以fit_transform一步到位
#X_dr = PCA(2).fit_transform(X)
plt.figure()
plt.scatter(X_dr[y==0, 0], X_dr[y==0, 1], c="red", label=iris.target_names[0]) 
plt.scatter(X_dr[y==1, 0], X_dr[y==1, 1], c="black", label=iris.target_names[1])
plt.scatter(X_dr[y==2, 0], X_dr[y==2, 1], c="orange", label=iris.target_names[2])
plt.legend()
plt.title('PCA of IRIS dataset')


y_train_pca=pca.transform(X_test) #获取新矩阵 （降维后的）

plt.figure()
plt.scatter(y_train_pca[y_pred==0, 0], y_train_pca[y_pred==0, 1], c="red", label=iris.target_names[0]) 
plt.scatter(y_train_pca[y_pred==1, 0], y_train_pca[y_pred==1, 1], c="black", label=iris.target_names[1])
plt.scatter(y_train_pca[y_pred==2, 0], y_train_pca[y_pred==2, 1], c="orange", label=iris.target_names[2])
plt.legend()
plt.title('predict of IRIS test_dataset')
plt.show()

KD树算法：

import math
import numpy as np
from sklearn.datasets import load_iris
from sklearn.model_selection import train_test_split
from sklearn.neighbors import KNeighborsClassifier
from sklearn.metrics import accuracy_score
from sklearn.decomposition import PCA # PCA主成分分析类
import matplotlib.pyplot as plt  # 画图工具
import pandas as pd
import time

# 加载鸢尾花数据集
iris = load_iris()
X = iris.data  # 特征向量

pts = X  #点集，任意维度的点集

 
class Node():
    def __init__(self,pt,leftBranch,rightBranch,dimension):
        self.pt = pt
        self.leftBranch = leftBranch
        self.rightBranch = rightBranch
        self.dimension = dimension
 
class KDTree():
    def __init__(self,data):
        self.nearestPt = None
        self.nearestDis = math.inf
    
    def createKDTree(self,currPts,dimension):
        if(len(currPts) == 0):
            return None
        mid = self.calMedium(currPts)
        sortedData = sorted(currPts,key=lambda x:x[dimension])
        leftBranch = self.createKDTree(sortedData[:mid],self.calDimension(dimension))
        rightBranch = self.createKDTree(sortedData[mid+1:],self.calDimension(dimension))
        return Node(sortedData[mid],leftBranch,rightBranch,dimension)
 
    def calMedium(self,currPts):
        return len(currPts) // 2
 
    def calDimension(self,dimension): # 区别就在于这里，几维就取余几
        return (dimension+1)%len(targetPt)
 
    def calDistance(self,p0,p1):
        return math.sqrt((p0[0]-p1[0])**2+(p0[1]-p1[1])**2)
 
    def getNearestPt(self,root,targetPt):
        self.search(root,targetPt)
        return self.nearestPt,self.nearestDis
        
    def search(self,node,targetPt):
        if node == None:
            return
        dist = node.pt[node.dimension] - targetPt[node.dimension]
        if(dist > 0):#目标点在节点的左侧或上侧
            self.search(node.leftBranch,targetPt)
        else:
            self.search(node.rightBranch,targetPt)
        tempDis = self.calDistance(node.pt,targetPt)
        if(tempDis < self.nearestDis):
            self.nearestDis = tempDis
            self.nearestPt = node.pt
        #回溯
        if(self.nearestDis > abs(dist)):
            if(dist > 0):
                self.search(node.rightBranch,targetPt)
            else:
                self.search(node.leftBranch,targetPt)
 


def get_min_distance(X,targetPt):
    small=math.sqrt(sum((X[0]-targetPt)**2))
    re_i=0
    index=0
    for point in X[1:]:
        d=math.sqrt(sum((point-targetPt)**2))
        if d<small:
            small=d
            re_i=index
        index=index+1
    return re_i

if __name__ == "__main__":
    targetPt = X[0]  #目标点，任意维度的点
    kdtree = KDTree(pts) 
    root = kdtree.createKDTree(pts,0)   


 
    # 记录开始时间
    start_time = time.time()

 
    for point in X:

         re_i = get_min_distance(X,point)
    
    # 记录结束时间
    end_time = time.time()
 
    # 计算并打印执行时间
    elapsed_time = end_time - start_time
    print(f"传统遍历方法执行时间: {elapsed_time}秒")
    # 记录开始时间
    start_time = time.time()

 
    for point in X:

         pt,minDis = kdtree.getNearestPt(root,point)
    # 记录结束时间
    end_time = time.time()
 
    # 计算并打印执行时间
    elapsed_time = end_time - start_time
    print(f"kd树执行时间: {elapsed_time}秒")

运行结果：

对了，这一次实验，其实对于KNN还少了几个实验，一个是k值得超参数实验，一个是KNN基于不同距离计算公示的考察。

原文地址：https://blog.csdn.net/weixin_43327597/article/details/137833530

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