Python实现KNN分类算法：原理、代码与鸢尾花数据集测试

#coding=utf-8
import math
#定义鸢尾花的数据类
class Iris:
 data=[]
 label=[]
 pass
#定义一个读取莺尾花数据集的函数
def load_dataset(filename="Iris_train.txt"):
 f=open(filename)
 line=f.readline().strip()
 propty=line.split(',')#属性名
 dataset=[]#保存每一个样本的数据信息
 label=[]#保存样本的标签
 while line:
 line=f.readline().strip()
 if(not line):
 break
 temp=line.split(',')
 content=[]
 for i in temp[0:-1]:
 content.append(float(i))
 dataset.append(content)
 label.append(temp[-1])
 total=Iris()
 total.data=dataset
 total.label=label
 return total#返回数据集
 
#定义一个Knn分类器类
class KnnClassifier:
 def __init__(self,k,type="Euler"):#初始化的时候定义正整数K和距离计算方式
 self.k=k
 self.type=type
 self.dataloaded=False
 def load_traindata(self,traindata):#加载数据集
 self.data=traindata.data
 self.label=traindata.label
 self.label_set=set(traindata.label)
 self.dataloaded=True#是否加载数据集的标记
 
 def Euler_dist(self,x,y):# 欧拉距离计算方法，x、y都是向量
 sum=0
 for i,j in zip(x,y):
 sum+=math.sqrt((i-j)**2)
 return sum
 def Manhattan_dist(self,x,y):#曼哈顿距离计算方法，x、y都是向量
 sum=0
 for i,j in zip(x,y):
 sum+=abs(i-j)
 return sum
 def predict(self,temp):#预测函数，读入一个预测样本的数据，temp是一个向量
 if(not self.dataloaded):#判断是否有训练数据
 print "No train_data load in"
 return
 distance_and_label=[]
 if(self.type=="Euler"):#判断距离计算方式，欧拉距离或者曼哈顿距离
 for i,j in zip(self.data,self.label):
 dist=self.Euler_dist(temp,i)
 distance_and_label.append([dist,j])
 else:
 if(self.type=="Manhattan"):
 for i,j in zip(self.data,self.label):
 dist=self.Manhattan_dist(temp,i)
 distance_and_label.append([dist,j])
 else:
 print "type choice error"
 #获取K个最邻近的样本的距离和类别标签
 neighborhood=sorted(distance_and_label,cmp=lambda x,y : cmp(x[0],y[0]))[0:self.k]
 neighborhood_class=[]
 for i in neighborhood:
 neighborhood_class.append(i[1])
 class_set=set(neighborhood_class)
 neighborhood_class_count=[]
 print "In k nearest neighborhoods:"
 #统计该K个最邻近点中各个类别的个数
 for i in class_set:
 a=neighborhood_class.count(i)
 neighborhood_class_count.append([i,a])
 print "class: ",i," count: ",a
 result=sorted(neighborhood_class_count,cmp=lambda x,y : cmp(x[1],y[1]))[-1][0]
 print "result: ",result
 return result#返回预测的类别
 
if __name__ == '__main__':
 traindata=load_dataset()#training data
 testdata=load_dataset("Iris_test.txt")#testing data
 #新建一个Knn分类器的K为20，默认为欧拉距离计算方式
 kc=KnnClassifier(20)
 kc.load_traindata(traindata)
 predict_result=[]
 #预测测试集testdata中所有待预测样本的结果
 for i,j in zip(testdata.data,testdata.label):
 predict_result.append([i,kc.predict(i),j])
 correct_count=0
 #将预测结果和正确结果进行比对，计算该次预测的准确率
 for i in predict_result:
 if(i[1]==i[2]):
 correct_count+=1
 ratio=float(correct_count)/len(predict_result)
 print "correct predicting ratio",ratio

In k nearest neighborhoods:
class: Iris-setosa count: 20
result: Iris-setosa
In k nearest neighborhoods:
class: Iris-setosa count: 20
result: Iris-setosa
In k nearest neighborhoods:
class: Iris-setosa count: 20
result: Iris-setosa
In k nearest neighborhoods:
class: Iris-setosa count: 20
result: Iris-setosa
In k nearest neighborhoods:
class: Iris-setosa count: 20
result: Iris-setosa
In k nearest neighborhoods:
class: Iris-versicolor count: 20
result: Iris-versicolor
In k nearest neighborhoods:
class: Iris-versicolor count: 20
result: Iris-versicolor
In k nearest neighborhoods:
class: Iris-versicolor count: 20
result: Iris-versicolor
In k nearest neighborhoods:
class: Iris-versicolor count: 20
result: Iris-versicolor
In k nearest neighborhoods:
class: Iris-versicolor count: 20
result: Iris-versicolor
In k nearest neighborhoods:
class: Iris-setosa count: 18
class: Iris-versicolor count: 2
result: Iris-setosa
correct predicting ratio 0.909090909091