1 数据集介绍：

虹膜

150个实例

萼片长度，萼片宽度，花瓣长度，花瓣宽度
(sepal length, sepal width, petal length and petal width）

类别：
Iris setosa, Iris versicolor, Iris virginica.

2. 利用Python的机器学习库sklearn: SkLearnExample.py

from sklearn import neighbors
from sklearn import datasets

knn = neighbors.KNeighborsClassifier()

iris = datasets.load_iris()

print iris

knn.fit(iris.data, iris.target)

predictedLabel = knn.predict([[0.1, 0.2, 0.3, 0.4]])

print predictedLabel

3. KNN 实现Implementation:

Example of kNN implemented from Scratch in Python

import csv
import random
import math
import operator

def loadDataset(filename, split, trainingSet=[] , testSet=[]):
with open(filename, 'rb') as csvfile:
lines = csv.reader(csvfile)
dataset = list(lines)
for x in range(len(dataset)-1):
for y in range(4):
dataset[x][y] = float(dataset[x][y])
if random.random() < split:
trainingSet.append(dataset[x])
else:
testSet.append(dataset[x])

def euclideanDistance(instance1, instance2, length):
distance = 0
for x in range(length):
distance += pow((instance1[x] - instance2[x]), 2)
return math.sqrt(distance)

def getNeighbors(trainingSet, testInstance, k):
distances = []
length = len(testInstance)-1
for x in range(len(trainingSet)):
dist = euclideanDistance(testInstance, trainingSet[x], length)
distances.append((trainingSet[x], dist))
distances.sort(key=operator.itemgetter(1))
neighbors = []
for x in range(k):
neighbors.append(distances[x][0])
return neighbors

def getResponse(neighbors):
classVotes = {}
for x in range(len(neighbors)):
response = neighbors[x][-1]
if response in classVotes:
classVotes[response] += 1
else:
classVotes[response] = 1
sortedVotes = sorted(classVotes.iteritems(), key=operator.itemgetter(1), reverse=True)
return sortedVotes[0][0]

def getAccuracy(testSet, predictions):
correct = 0
for x in range(len(testSet)):
if testSet[x][-1] == predictions[x]:
correct += 1
return (correct/float(len(testSet))) * 100.0

def main():
# prepare data
trainingSet=[]
testSet=[]
split = 0.67
loadDataset(r'D:\MaiziEdu\DeepLearningBasics_MachineLearning\Datasets\iris.data.txt', split, trainingSet, testSet)
print 'Train set: ' + repr(len(trainingSet))
print 'Test set: ' + repr(len(testSet))
# generate predictions
predictions=[]
k = 3
for x in range(len(testSet)):
neighbors = getNeighbors(trainingSet, testSet[x], k)
result = getResponse(neighbors)
predictions.append(result)
print('> predicted=' + repr(result) + ', actual=' + repr(testSet[x][-1]))
accuracy = getAccuracy(testSet, predictions)
print('Accuracy: ' + repr(accuracy) + '%')

main()