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机器学习—决策树

时间:2018-04-12 23:01:43      阅读:294      评论:0      收藏:0      [点我收藏+]

一、原理部分:

还是图片显示~

 技术分享图片

技术分享图片

技术分享图片 

二、sklearn实现

1、回归树

import pandas as pd
import numpy as np
import matplotlib.pyplot as plt
import matplotlib as mpl
import seaborn as sns
mpl.rcParams[font.sans-serif] = [uSimHei]
mpl.rcParams[axes.unicode_minus] = False
from sklearn.model_selection import train_test_split
from sklearn.metrics import mean_squared_error

#制造一些数据
x_data = np.random.rand(200,5)*10
w = np.array([2,4,6,8,10])
y = np.dot(x_data,w) + np.random.rand(200)*20 + 20
x_train,x_test,y_train,y_test = train_test_split(x_data,y)

#先试试决策回归树吧,都没试过
from sklearn.tree import DecisionTreeRegressor
dtr = DecisionTreeRegressor()
dtr.fit(x_train,y_train)
y_hat = dtr.predict(x_test)
print(决策回归树的误差:,mean_squared_error(y_test,y_hat))

#画图
fig,ax = plt.subplots()
fig.set_size_inches(10,6)
ax.plot(np.arange(len(y_hat)),y_hat,color = r)
ax.plot(np.arange(len(y_hat)),y_test,color = g)

决策树做回归也太差了吧,难道是我调参有问题吗?一会试试调参看看

决策回归树的误差: 667.87208618

技术分享图片

#调参一下试试
from sklearn.model_selection import GridSearchCV
model_dtr = GridSearchCV(dtr,param_grid=({max_depth:np.arange(1,50)}),cv=10)
model_dtr.fit(x_train,y_train)
y_hat = model_dtr.predict(x_test)
print(model_dtr.best_params_)
print(决策回归树的误差:,mean_squared_error(y_test,y_hat))

还是没啥用,好差的效果,同样的数据,前面线性回归的均方误差才二十几

决策回归树的误差: 643.989924585

 2、分类树

from sklearn.datasets import load_digits
from sklearn.tree import DecisionTreeClassifier
from sklearn.metrics import accuracy_score
digits = load_digits()
x_data = digits.data
y_data = digits.target
x_train,x_test,y_train,y_test = train_test_split(x_data,y_data)
dtc = DecisionTreeClassifier()
dtc.fit(x_train,y_train)
y_hat = dtc.predict(x_test)
print(正确率,accuracy_score(y_hat,y_test))


#调个参数看看
model_dtc = GridSearchCV(dtc,param_grid=({max_depth:np.arange(1,20)}),cv=10)
model_dtc.fit(x_train,y_train)
print(最佳参数,model_dtc.best_params_)
y_hat = model_dtc.predict(x_test)
y_hat = dtc.predict(x_test)
print(正确率,accuracy_score(y_hat,y_test))

 

 正确率 0.817777777778

最佳参数 {‘max_depth‘: 18}
正确率 0.817777777778

决策树还是弱分类器啊,难怪都喜欢用它来做ensemble

 

机器学习—决策树

原文:https://www.cnblogs.com/slowlyslowly/p/8810958.html

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