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這篇文章主要講解了“python怎么實(shí)現(xiàn)K最近鄰居”,文中的講解內(nèi)容簡單清晰,易于學(xué)習(xí)與理解,下面請大家跟著小編的思路慢慢深入,一起來研究和學(xué)習(xí)“python怎么實(shí)現(xiàn)K最近鄰居”吧!
它可以用于分類和回歸問題。但是,它更廣泛地用于行業(yè)中的分類問題。K個最近鄰居是一種簡單的算法,可以存儲所有可用案例,并通過其k個鄰居的多數(shù)票對新案例進(jìn)行分類。在用距離函數(shù)測量的K個最近鄰居中,分配給該類別的案例最為常見。
這些距離函數(shù)可以是歐幾里得距離,曼哈頓距離,明可夫斯基距離和漢明距離。前三個函數(shù)用于連續(xù)函數(shù),第四個函數(shù)用于分類變量。如果K = 1,則將案例簡單分配給其最近鄰居的類別。有時,執(zhí)行kNN建模時選擇K確實(shí)是一個挑戰(zhàn)。
KNN可以輕松地映射到我們的現(xiàn)實(shí)生活。如果您想了解一個沒有信息的人,則可能想了解他的密友和他所進(jìn)入的圈子并獲得他/她的信息!
選擇kNN之前要考慮的事項(xiàng):
KNN在計(jì)算上很昂貴
變量應(yīng)歸一化,否則較大范圍的變量可能會產(chǎn)生偏差
在進(jìn)行kNN處理之前(例如離群值,噪聲消除),在預(yù)處理階段進(jìn)行更多工作
下面來看使用Python實(shí)現(xiàn)的案例:
# importing required libraries
import pandas as pd
from sklearn.neighbors import KNeighborsClassifier
from sklearn.metrics import accuracy_score
train_data = pd.read_csv('train-data.csv')
test_data = pd.read_csv('test-data.csv')
print('Shape of training data :',train_data.shape)
print('Shape of testing data :',test_data.shape)
train_x = train_data.drop(columns=['Survived'],axis=1)
train_y = train_data['Survived']
test_x = test_data.drop(columns=['Survived'],axis=1)
test_y = test_data['Survived']
'''
sklearn K-Neighbors Classifier:
https://scikit-learn.org/stable/modules/generated/
sklearn.neighbors.KNeighborsClassifier.html
'''
model = KNeighborsClassifier()
model.fit(train_x,train_y)
print('\nThe number of neighbors used to predict the target : '\
,model.n_neighbors)
predict_train = model.predict(train_x)
print('\nTarget on train data',predict_train)
accuracy_train = accuracy_score(train_y,predict_train)
print('accuracy_score on train dataset : ', accuracy_train)
predict_test = model.predict(test_x)
print('Target on test data',predict_test)
accuracy_test = accuracy_score(test_y,predict_test)
print('accuracy_score on test dataset : ', accuracy_test)
運(yùn)行結(jié)果:
Shape of training data : (712, 25)
Shape of testing data : (179, 25)
The number of neighbors used to predict the target : 5
Target on train data [0 1 1 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 1 1 0 1 0 0 0 0
1 0 0 0 0 0 1 1 1 1 0 1 0 0 0 0 0 0 0 0 0 1 0 1 1 1 1 0 1 0 1 0 0 0 0 0 0
0 1 1 0 0 0 0 0 1 0 1 0 0 0 1 1 1 0 1 0 0 0 0 0 1 0 0 1 0 1 1 1 0 1 0 1 0
0 1 1 0 1 0 0 1 0 0 0 0 1 0 0 1 1 0 0 1 0 0 0 1 1 0 1 0 0 0 1 0 0 0 1 0 0
0 0 0 1 1 0 0 1 0 0 1 0 1 0 0 1 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1
0 0 1 1 1 0 0 1 0 1 0 0 0 1 1 1 0 0 0 1 1 1 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0
0 0 1 0 0 0 1 0 1 0 0 0 0 1 0 1 0 0 0 1 0 1 0 0 1 0 0 0 1 1 0 1 0 0 0 0 0
1 1 1 1 1 0 1 1 1 1 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 1 1 0 0 0 1 0 0 0 1 0 0
0 0 0 0 0 1 1 0 0 0 1 0 0 0 0 0 1 1 1 1 0 0 0 0 1 0 1 0 0 0 1 1 0 1 0 0 1
1 0 0 1 0 0 1 0 0 0 0 0 1 0 0 0 1 0 0 0 0 1 1 1 1 0 0 0 0 1 0 0 0 1 0 1 0
0 0 0 1 0 0 1 0 0 1 0 1 0 0 1 0 0 1 0 0 1 1 1 1 0 0 1 1 0 1 0 1 0 1 1 1 1
0 1 1 1 0 0 0 0 0 0 1 0 1 0 0 1 0 0 1 1 1 0 0 0 1 0 1 0 0 1 0 0 0 0 1 0 0
0 1 0 0 0 0 0 0 1 0 0 1 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 1 1 1 0 0 0 0 1 0
0 0 0 1 1 0 0 0 0 1 1 0 0 0 1 0 1 1 1 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 1 1 1
1 0 0 0 0 1 0 0 0 1 1 0 0 0 1 1 1 0 0 0 0 0 1 1 0 0 0 0 1 1 1 1 0 1 0 0 0
0 1 1 1 1 0 0 1 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 0 1 1 0 0 0 1 1 1 0 1 1 1 0
1 0 0 0 0 1 0 1 0 1 0 1 1 0 0 1 0 1 1 0 1 0 0 0 1 0 1 1 0 0 0 0 1 0 0 0 1
0 0 0 1 0 1 0 1 0 0 1 1 0 0 0 0 1 0 0 0 0 0 0 1 1 1 0 1 0 0 0 1 0 1 0 0 0
1 1 0 0 0 0 0 1 0 0 1 0 1 0 0 1 1 0 0 0 1 0 1 0 0 1 1 0 0 0 1 0 0 1 0 1 0
1 0 1 1 1 0 0 1 0]
accuracy_score on train dataset : 0.8047752808988764
Target on test data [0 0 0 1 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1 0 0 0 0 1 0 1 0 0
1 0 0 1 1 0 0 0 1 0 0 1 1 1 0 0 0 1 1 0 0 0 0 0 1 1 0 0 0 1 0 0 0 1 0 0 0
1 0 0 0 0 0 0 0 0 0 0 0 1 1 1 0 0 0 1 0 1 0 0 0 1 0 1 1 0 1 1 0 0 1 0 0 1
0 1 0 0 1 0 1 0 1 1 0 1 0 0 1 1 0 0 1 0 0 0 1 1 0 0 0 1 0 1 0 1 0 0 0 0 0
0 0 0 0 1 0 0 0 0 1 0 0 0 1 0 0 0 1 1 0 1 0 1 0 0 1 0 0 0 0 0]
accuracy_score on test dataset : 0.7150837988826816
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