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随机森林random forest及python实现

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引言

随机森林能够用来获取数据的主要特征,进行分类、回归任务。

1. 随机森林及其特点

根据个体学习器的生成方式,目前的集成学习方法大致可分为两大类,即个体学习器之间存在强依赖关系,必须串行生成的序列化方法,以及个体学习器间不存在强依赖关系,可同时生成的并行化方法;前者的代表是Boosting,后者的代表是Bagging

随机森林在以决策树为基学习器构建Bagging集成的基础上,进一步在决策树的训练过程中引入了随机属性选择(即引入随机特征选择)。

简单来说,随机森林就是对决策树的Bagging集成。

特点:
1、随机选择样本(放回抽样);
2、随机选择特征;
3、构建决策树;
4、随机森林投票(平均)。

举例:

比如预测salary,就是构建多个决策树job,age,house,然后根据要预测的量的各个特征(job = teacher,age = 39,house = suburb)分别在对应决策树的目标值概率( P ( s a l a r y < 5000 ∣ j o b = t e a c h e r ) P(salary<5000| job = teacher) P(salary<5000job=teacher) ),从而确定预测量的发生概率(如最终预测出 P ( s a l a r y < 5000 ) = 0.3 P(salary<5000)=0.3 P(salary<5000)=0.3 ).

随机森林参数说明:

最主要的两个参数是n_estimatorsmax_features

1.n_estimators:表示森林里树的个数。

理论上是越大越好,但是计算时间也相应增长。所以,并不是取得越大就会越好,预测效果最好的将会出现在合理的树个数。

2.max_features:每个决策树的随机选择的特征数目。

每个决策树在随机选择的这max_features特征里找到某个“最佳”特征,使得模型在该特征的某个值上分裂之后得到的收益最大化。max_features越少,方差就会减少,但同时偏差就会增加。
如果是回归问题,则max_features=n_features,如果是分类问题,则max_features=sqrt(n_features),其中,n_features 是输入特征数。

其他参数:

3.max_depth: 树的最深深度。

如果max_depth=None,节点会拟合到增益为0,或者所有的叶节点含有小于min_samples_split个样本。如果同时min_sample_split=1, 决策树会拟合得很深,甚至会过拟合。

4.bootstrap:自助法,默认为True。

如果bootstrap==True,将每次有放回地随机选取样本。
只有在extra-trees中,bootstrap=False

Extra trees,Extremely Randomized Trees,指极度随机树,和随机森林区别是:

1、随机森林应用的是Bagging模型,而ET是使用所有的训练样本得到每棵决策树,也就是每棵决策树应用的是相同的全部训练样本

2、随机森林是在一个随机子集内得到最佳分叉属性,而ET是完全随机的得到分叉值,从而实现对决策树进行分叉的。

训练随机森林时,建议使用cross_validated(交叉验证),把数据n等份,每次取其中一份当验证集,其余数据训练随机森林,并用于预测测试集。最终得到n个结果,并平均得到最终结果。

2、随机森林python实现

2.1 随机森林回归器的使用Demo1

实现随机森林基本功能

#随机森林

from sklearn.tree import DecisionTreeRegressor  
from sklearn.ensemble import RandomForestRegressor  
import numpy as np  
   
from sklearn.datasets import load_iris  
iris=load_iris()  
#print iris#iris的4个属性是:萼片宽度 萼片长度 花瓣宽度 花瓣长度 标签是花的种类:setosa versicolour virginica  
print(iris['target'].shape)
rf=RandomForestRegressor()#这里使用了默认的参数设置  
rf.fit(iris.data[:150],iris.target[:150])#进行模型的训练  

#随机挑选两个预测不相同的样本  
instance=iris.data[[100,109]]  
print(instance)
rf.predict(instance[[0]])
print('instance 0 prediction;',rf.predict(instance[[0]]))
print( 'instance 1 prediction;',rf.predict(instance[[1]]))
print(iris.target[100],iris.target[109])  

运行结果

(150,)
[[ 6.3  3.3  6.   2.5]
 [ 7.2  3.6  6.1  2.5]]
instance 0 prediction; [ 2.]
instance 1 prediction; [ 2.]
2 2

2.2 随机森林分类器、决策树、extra树分类器的比较Demo2

3种方法的比较

#random forest test

from sklearn.model_selection import cross_val_score
from sklearn.datasets import make_blobs
from sklearn.ensemble import RandomForestClassifier
from sklearn.ensemble import ExtraTreesClassifier
from sklearn.tree import DecisionTreeClassifier

X, y = make_blobs(n_samples=10000, n_features=10, centers=100,random_state=0)

clf = DecisionTreeClassifier(max_depth=None, min_samples_split=2,random_state=0)
scores = cross_val_score(clf, X, y)
print(scores.mean())                             


clf = RandomForestClassifier(n_estimators=10, max_depth=None,min_samples_split=2, random_state=0)
scores = cross_val_score(clf, X, y)
print(scores.mean())                             

clf = ExtraTreesClassifier(n_estimators=10, max_depth=None,min_samples_split=2, random_state=0)
scores = cross_val_score(clf, X, y)
print(scores.mean())

运行结果:

0.979408793821 #DecisionTreeClassifier
0.999607843137 #RandomForestClassifier
0.999898989899 #ExtraTreesClassifier

2.3 随机森林回归器regressor-实现特征选择

#随机森林2
from sklearn.tree import DecisionTreeRegressor  
from sklearn.ensemble import RandomForestRegressor  
import numpy as np  
   
from sklearn.datasets import load_iris  
iris=load_iris()  

from sklearn.model_selection import cross_val_score, ShuffleSplit  
X = iris["data"]  
Y = iris["target"]  
names = iris["feature_names"]  

rf = RandomForestRegressor()  
scores = []  
for i in range(X.shape[1]):  
     score = cross_val_score(rf, X[:, i:i+1], Y, scoring="r2",  
                              cv=ShuffleSplit(len(X), 3, .3))  
     scores.append((round(np.mean(score), 3), names[i]))  
     
print(sorted(scores, reverse=True))

运行结果:

[(0.89300000000000002, 'petal width (cm)'), (0.82099999999999995, 'petal length
(cm)'), (0.13, 'sepal length (cm)'), (-0.79100000000000004, 'sepal width (cm)')]

2.4 demo4-随机森林
本来想利用以下代码来构建随机随机森林决策树,但是,遇到的问题是,程序一直在运行,无法响应,还需要调试。

#随机森林4
#coding:utf-8  
import csv  
from random import seed  
from random import randrange  
from math import sqrt  
  
def loadCSV(filename):#加载数据,一行行的存入列表  
    dataSet = []  
    with open(filename, 'r') as file:  
        csvReader = csv.reader(file)  
        for line in csvReader:  
            dataSet.append(line)  
    return dataSet  
  
# 除了标签列,其他列都转换为float类型  
def column_to_float(dataSet):  
    featLen = len(dataSet[0]) - 1  
    for data in dataSet:  
        for column in range(featLen):  
            data[column] = float(data[column].strip())  
  
# 将数据集随机分成N块,方便交叉验证,其中一块是测试集,其他四块是训练集  
def spiltDataSet(dataSet, n_folds):  
    fold_size = int(len(dataSet) / n_folds)  
    dataSet_copy = list(dataSet)  
    dataSet_spilt = []  
    for i in range(n_folds):  
        fold = []  
        while len(fold) < fold_size:  # 这里不能用if,if只是在第一次判断时起作用,while执行循环,直到条件不成立  
            index = randrange(len(dataSet_copy))  
            fold.append(dataSet_copy.pop(index))  # pop() 函数用于移除列表中的一个元素(默认最后一个元素),并且返回该元素的值。  
        dataSet_spilt.append(fold)  
    return dataSet_spilt  
  
# 构造数据子集  
def get_subsample(dataSet, ratio):  
    subdataSet = []  
    lenSubdata = round(len(dataSet) * ratio)#返回浮点数  
    while len(subdataSet) < lenSubdata:  
        index = randrange(len(dataSet) - 1)  
        subdataSet.append(dataSet[index])  
    # print len(subdataSet)  
    return subdataSet  
  
# 分割数据集  
def data_spilt(dataSet, index, value):  
    left = []  
    right = []  
    for row in dataSet:  
        if row[index] < value:  
            left.append(row)  
        else:  
            right.append(row)  
    return left, right  
  
# 计算分割代价  
def spilt_loss(left, right, class_values):  
    loss = 0.0  
    for class_value in class_values:  
        left_size = len(left)  
        if left_size != 0:  # 防止除数为零  
            prop = [row[-1] for row in left].count(class_value) / float(left_size)  
            loss += (prop * (1.0 - prop))  
        right_size = len(right)  
        if right_size != 0:  
            prop = [row[-1] for row in right].count(class_value) / float(right_size)  
            loss += (prop * (1.0 - prop))  
    return loss  
  
# 选取任意的n个特征,在这n个特征中,选取分割时的最优特征  
def get_best_spilt(dataSet, n_features):  
    features = []  
    class_values = list(set(row[-1] for row in dataSet))  
    b_index, b_value, b_loss, b_left, b_right = 999, 999, 999, None, None  
    while len(features) < n_features:  
        index = randrange(len(dataSet[0]) - 1)  
        if index not in features:  
            features.append(index)  
    # print 'features:',features  
    for index in features:#找到列的最适合做节点的索引,(损失最小)  
        for row in dataSet:  
            left, right = data_spilt(dataSet, index, row[index])#以它为节点的,左右分支  
            loss = spilt_loss(left, right, class_values)  
            if loss < b_loss:#寻找最小分割代价  
                b_index, b_value, b_loss, b_left, b_right = index, row[index], loss, left, right  
    # print b_loss  
    # print type(b_index)  
    return {
   'index': b_index, 'value': b_value, 'left': b_left, 'right': b_right}  
  
# 决定输出标签  
def decide_label(data):  
    output = [row[-1] for row in data]  
    return max(set(output), key=output.count)  
  
  
# 子分割,不断地构建叶节点的过程对对对  
def sub_spilt(root, n_features, max_depth, min_size, depth):  
    left = root['left']  
    # print left  
    right = root['right']  
    del (root['left'])  
    del (root['right'])  
    # print depth  
    if not left or not right:  
        root['left'] = root['right'] = decide_label(left + right)  
        # print 'testing'  
        return  
    if depth > max_depth:  
        root['left'] = decide_label(left)  
        root['right'] = decide_label(right)  
        return  
    if len(left) < min_size:  
        root['left'] = decide_label(left)  
    else:  
        root['left'] = get_best_spilt(left, n_features)  
        # print 'testing_left'  
        sub_spilt(root['left'], n_features, max_depth, min_size, depth + 1)  
    if len(right) < min_size:  
        root['right'] = decide_label(right)  
    else:  
        root['right'] = get_best_spilt(right, n_features)  
        # print 'testing_right'  
        sub_spilt(root['right'], n_features, max_depth, min_size, depth + 1)  
  
        # 构造决策树  
def build_tree(dataSet, n_features, max_depth, min_size):  
    root = get_best_spilt(dataSet, n_features)  
    sub_spilt(root, n_features, max_depth, min_size, 1)  
    return root  
# 预测测试集结果  
def predict(tree, row):  
    predictions = []  
    if row[tree['index']] < tree['value']:  
        if isinstance(tree['left'], dict):  
            return predict(tree['left'], row)  
        else:  
            return tree['left']  
    else:  
        if isinstance(tree['right'], dict):  
            return predict(tree['right'], row)  
        else:  
            return tree['right']  
            # predictions=set(predictions)  
def bagging_predict(trees, row):  
    predictions = [predict(tree, row) for tree in trees]  
    return max(set(predictions), key=predictions.count)  
# 创建随机森林  
def random_forest(train, test, ratio, n_feature, max_depth, min_size, n_trees):  
    trees = []  
    for i in range(n_trees):  
        train = get_subsample(train, ratio)#从切割的数据集中选取子集  
        tree = build_tree(train, n_features, max_depth, min_size)  
        # print 'tree %d: '%i,tree  
        trees.append(tree)  
    # predict_values = [predict(trees,row) for row in test]  
    predict_values = [bagging_predict(trees, row) for row in test]  
    return predict_values  
# 计算准确率  
def accuracy(predict_values, actual):  
    correct = 0  
    for i in range(len(actual)):  
        if actual[i] == predict_values[i]:  
            correct += 1  
    return correct / float(len(actual))  
  
  
if __name__ == '__main__':  
    seed(1)  
    dataSet = loadCSV(r'G:\训练小样本2.csv')  
    column_to_float(dataSet)  
    n_folds = 5  
    max_depth = 15  
    min_size = 1  
    ratio = 1.0  
    # n_features=sqrt(len(dataSet)-1)  
    n_features = 15  
    n_trees = 10  
    folds = spiltDataSet(dataSet, n_folds)#先是切割数据集  
    scores = []  
    for fold in folds:  
   		 # 此处不能简单地用train_set=folds,这样用属于引用,那么当train_set的值改变的时候,folds的值也会改变,所以要用复制的形式。
   		 #(L[:])能够复制序列,D.copy() 能够复制字典,list能够生成拷贝 list(L)  
        train_set = folds[:]  
        train_set.remove(fold)#选好训练集  
        train_set = sum(train_set, [])  # 将多个fold列表组合成一个train_set列表  
        test_set = []  
        for row in fold:  
            row_copy = list(row)  
            row_copy[-1] = None  
            test_set.append(row_copy)  
            # for row in test_set:  
            # print row[-1]  
        actual = [row[-1] for row in fold]  
        predict_values = random_forest(train_set, test_set, ratio, n_features, max_depth, min_size, n_trees)  
        accur = accuracy(predict_values, actual)  
        scores.append(accur)  
    print ('Trees is %d' % n_trees)  
    print ('scores:%s' % scores)  
    print ('mean score:%s' % (sum(scores) / float(len(scores))))  

2.5 随机森林分类sonic data

# CART on the Bank Note dataset
from random import seed
from random import randrange
from csv import reader

# Load a CSV file
def load_csv(filename):
	file = open(filename, "r")
	lines = reader(file)
	dataset = list(lines)
	return dataset

# Convert string column to float
def str_column_to_float(dataset, column):
	for row in dataset:
		row[column] = float(row[column].strip())

# Split a dataset into k folds
def cross_validation_split(dataset, n_folds):
	dataset_split = list()
	dataset_copy = list(dataset)
	fold_size = int(len(dataset) / n_folds)
	for i in range(n_folds):
		fold = list()
		while len(fold) < fold_size:
			index = randrange(len(dataset_copy))
			fold.append(dataset_copy.pop(index))
		dataset_split.append(fold)
	return dataset_split

# Calculate accuracy percentage
def accuracy_metric(actual, predicted):
	correct = 0
	for i in range(len(actual)):
		if actual[i] == predicted[i]:
			correct += 1
	return correct / float(len(actual)) * 100.0

# Evaluate an algorithm using a cross validation split
def evaluate_algorithm(dataset, algorithm, n_folds, *args):
	folds = cross_validation_split(dataset, n_folds)
	scores = list()
	for fold in folds:
		train_set = list(folds)
		train_set.remove(fold)
		train_set = sum(train_set, [])
		test_set = list()
		for row in fold:
			row_copy = list(row)
			test_set.append(row_copy)
			row_copy[-1] = None
		predicted = algorithm(train_set, test_set, *args)
		actual = [row[-1] for row in fold]
		accuracy = accuracy_metric(actual, predicted)
		scores.append(accuracy)
	return scores

# Split a data set based on an attribute and an attribute value
def test_split(index, value, dataset):
	left, right = list(), list()
	for row in dataset:
		if row[index] < value:
			left.append(row)
		else:
			right.append(row)
	return left, right

# Calculate the Gini index for a split dataset
def gini_index(groups, class_values):
	gini = 0.0
	for class_value in class_values:
		for group in groups:
			size = len(group)
			if size == 0:
				continue
			proportion = [row[-1] for row in group].count(class_value) / float(size)
			gini += (proportion * (1.0 - proportion))
	return gini

# Select the best split point for a dataset
def get_split(dataset):
	class_values = list(set(row[-1] for row in dataset))
	b_index, b_value, b_score, b_groups = 999, 999, 999, None
	for index in range(len(dataset[0])-1):
		for row in dataset:
			groups = test_split(index, row[index], dataset)
			gini = gini_index(groups, class_values)
			if gini < b_score:
				b_index, b_value, b_score, b_groups = index, row[index], gini, groups
	print ({
   'index':b_index, 'value':b_value})
	return {
   'index':b_index, 'value':b_value, 'groups':b_groups}

# Create a terminal node value
def to_terminal(group):
	outcomes = [row[-1] for row in group]
	return max(set(outcomes), key=outcomes.count)

# Create child splits for a node or make terminal
def split(node, max_depth, min_size, depth):
	left, right = node['groups']
	del(node['groups'])
	# check for a no split
	if not left or not right:
		node['left'] = node['right'] = to_terminal(left + right)
		return
	# check for max depth
	if depth >= max_depth:
		node['left'], node['right'] = to_terminal(left), to_terminal(right)
		return
	# process left child
	if len(left) <= min_size:
		node['left'] = to_terminal(left)
	else:
		node['left'] = get_split(left)
		split(node['left'], max_depth, min_size, depth+1)
	# process right child
	if len(right) <= min_size:
		node['right'] = to_terminal(right)
	else:
		node['right'] = get_split(right)
		split(node['right'], max_depth, min_size, depth+1)

# Build a decision tree
def build_tree(train, max_depth, min_size):
	root = get_split(train)
	split(root, max_depth, min_size, 1)
	return root

# Make a prediction with a decision tree
def predict(node, row):
	if row[node['index']] < node['value']:
		if isinstance(node['left'], dict):
			return predict(node['left'], row)
		else:
			return node['left']
	else:
		if isinstance(node['right'], dict):
			return predict(node['right'], row)
		else:
			return node['right']

# Classification and Regression Tree Algorithm
def decision_tree(train, test, max_depth, min_size):
	tree = build_tree(train, max_depth, min_size)
	predictions = list()
	for row in test:
		prediction = predict(tree, row)
		predictions.append(prediction)
	return(predictions)

# Test CART on Bank Note dataset
seed(1)
# load and prepare data
filename = r'G:\0pythonstudy\决策树\sonar.all-data.csv'
dataset = load_csv(filename)
# convert string attributes to integers
for i in range(len(dataset[0])-1):
	str_column_to_float(dataset, i)
# evaluate algorithm
n_folds = 5
max_depth = 5
min_size = 10
scores = evaluate_algorithm(dataset, decision_tree, n_folds, max_depth, min_size)
print('Scores: %s' % scores)
print('Mean Accuracy: %.3f%%' % (sum(scores)/float(len(scores))))

运行结果:

{
   'index': 38, 'value': 0.0894}
{
   'index': 36, 'value': 0.8459}
{
   'index': 50, 'value': 0.0024}
{
   'index': 15, 'value': 0.0906}
{
   'index': 16, 'value': 0.9819}
{
   'index': 10, 'value': 0.0785}
{
   'index': 16, 'value': 0.0886}
{
   'index': 38, 'value': 0.0621}
{
   'index': 5, 'value': 0.0226}
{
   'index': 8, 'value': 0.0368}
{
   'index': 11, 'value': 0.0754}
{
   'index': 0, 'value': 0.0239}
{
   'index': 8, 'value': 0.0368}
{
   'index': 29, 'value': 0.1671}
{
   'index': 46, 'value': 0.0237}
{
   'index': 38, 'value': 0.0621}
{
   'index': 14, 'value': 0.0668}
{
   'index': 4, 'value': 0.0167}
{
   'index': 37, 'value': 0.0836}
{
   'index': 12, 'value': 0.0616}
{
   'index': 7, 'value': 0.0333}
{
   'index': 33, 'value': 0.8741}
{
   'index': 16, 'value': 0.0886}
{
   'index': 8, 'value': 0.0368}
{
   'index': 33, 'value': 0.0798}
{
   'index': 44, 'value': 0.0298}
Scores: [48.78048780487805, 70.73170731707317, 58.536585365853654, 51.2195121951
2195, 39.02439024390244]
Mean Accuracy: 53.659%

知识点:
1.load CSV file

from csv import reader
# Load a CSV file
def load_csv(filename):
	file = open(filename, "r")
	lines = reader(file)
	dataset = list(lines)
	return dataset

filename = r'G:\0pythonstudy\决策树\sonar.all-data.csv'
dataset=load_csv(filename)
print(dataset)

2.把数据转化成float格式

# Convert string column to float
def str_column_to_float(dataset, column):
    for row in dataset:
        row[column] = float(row[column].strip())
    # print(row[column])

# convert string attributes to integers
for i in range(len(dataset[0])-1):
	str_column_to_float(dataset, i)

3.把最后一列的分类字符串转化成0、1整数

def str_column_to_int(dataset, column):
   class_values = [row[column] for row in dataset]#生成一个class label的list
   # print(class_values)
   unique = set(class_values)#set 获得list的不同元素
   print(unique)
   
   lookup = dict()#定义一个字典
   # print(enumerate(unique))
   for i, value in enumerate(unique):
       lookup[value] = i
   # print(lookup)
   for row in dataset:
       row[column] = lookup[row[column]]
   print(lookup['M'])

4、把数据集分割成K份

# Split a dataset into k folds
def cross_validation_split(dataset, n_folds):
	dataset_split = list()#生成空列表
	
	dataset_copy = list(dataset)
	print(len(dataset_copy))
	print(len(dataset))
	#print(dataset_copy)
	fold_size = int(len(dataset) / n_folds)
	for i in range(n_folds):
		fold = list()
		while len(fold) < fold_size:
			index = randrange(len(dataset_copy))
			# print(index)
			fold.append(dataset_copy.pop(index))#使用.pop()把里边的元素都删除(相当于转移),这k份元素各不相同。
		dataset_split.append(fold)
	return dataset_split

n_folds=5   
folds = cross_validation_split(dataset, n_folds)#k份元素各不相同的训练集

5.计算正确率

# Calculate accuracy percentage
def accuracy_metric(actual, predicted):
	correct = 0
	for i in range(len(actual)):
		if actual[i] == predicted[i]:
			correct += 1
	return correct / float(len(actual)) * 100.0#这个是二值分类正确性的表达式

6.二分类每列

# Split a data set based on an attribute and an attribute value
def test_split(index, value, dataset):
	left, right = list(), list()#初始化两个空列表
	for row in dataset:
		if row[index] < value:
			left.append(row)
		else:
			right.append(row)
	return left, right #返回两个列表,每个列表以value为界限对指定行(index)进行二分类。

7.使用gini系数来获得最佳分割点

# Calculate the Gini index for a split dataset
def gini_index(groups, class_values):
	gini = 0.0
	for class_value in class_values:
		for group in groups:
			size = len(group)
			if size == 0:
				continue
			proportion = [row[-1] for row in group].count(class_value) / float(size)
			gini += (proportion * (1.0 - proportion))
	return gini

# Select the best split point for a dataset
def get_split(dataset):
	class_values = list(set(row[-1] for row in dataset))
	b_index, b_value, b_score, b_groups = 999, 999, 999, None
	for index in range(len(dataset[0])-1):
		for row in dataset:
			groups = test_split(index, row[index], dataset)
			gini = gini_index(groups, class_values)
			if gini < b_score:
				b_index, b_value, b_score, b_groups = index, row[index], gini, groups
	# print(groups)
	print ({
   'index':b_index, 'value':b_value,'score':gini})
	return {
   'index':b_index, 'value':b_value, 'groups':b_groups}

这段代码,在求gini指数,直接应用定义式,不难理解。获得最佳分割点可能比较难看懂,这里用了两层迭代,一层是对不同列的迭代,一层是对不同行的迭代。并且,每次迭代,都对gini系数进行更新。

8、决策树生成

# Create child splits for a node or make terminal
def split(node, max_depth, min_size, depth):
	left, right = node['groups']
	del(node['groups'])
	# check for a no split
	if not left or not right:
		node['left'] = node['right'] = to_terminal(left + right)
		return
	# check for max depth
	if depth >= max_depth:
		node['left'], node['right'] = to_terminal(left), to_terminal(right)
		return
	# process left child
	if len(left) <= min_size:
		node['left'] = to_terminal(left)
	else:
		node['left'] = get_split(left)
		split(node['left'], max_depth, min_size, depth+1)
	# process right child
	if len(right) <= min_size:
		node['right'] = to_terminal(right)
	else:
		node['right'] = get_split(right)
		split(node['right'], max_depth, min_size, depth+1)

这里使用了递归编程,不断生成左叉树和右叉树。

9.构建决策树

# Build a decision tree
def build_tree(train, max_depth, min_size):
	root = get_split(train)
	split(root, max_depth, min_size, 1)
	return root	
	
tree=build_tree(train_set, max_depth, min_size)
print(tree)

10、预测test集

# Build a decision tree
def build_tree(train, max_depth, min_size):
	root = get_split(train)#获得最好的分割点,下标值,groups
	split(root, max_depth, min_size, 1)
	return root	
	
# tree=build_tree(train_set, max_depth, min_size)
# print(tree)		




# Make a prediction with a decision tree
def predict(node, row):
	print(row[node['index']])
	print(node['value'])
	if row[node['index']] < node['value']:#用测试集来代入训练的最好分割点,分割点有偏差时,通过搜索左右叉树来进一步比较。
		if isinstance(node['left'], dict):#如果是字典类型,执行操作
			return predict(node['left'], row)
		else:
			return node['left']
	else:
		if isinstance(node['right'], dict):
			return predict(node['right'], row)
		else:
			return node['right']

tree = build_tree(train_set, max_depth, min_size)
predictions = list()
for row in test_set:
	prediction = predict(tree, row)
	predictions.append(prediction)

11.评价决策树

# Evaluate an algorithm using a cross validation split
def evaluate_algorithm(dataset, algorithm, n_folds, *args):
	folds = cross_validation_split(dataset, n_folds)
	scores = list()
	for fold in folds:
		train_set = list(folds)
		train_set.remove(fold)
		train_set = sum(train_set, [])
		test_set = list()
		for row in fold:
			row_copy = list(row)
			test_set.append(row_copy)
			row_copy[-1] = None
		predicted = algorithm(train_set, test_set, *args)
		actual = [row[-1] for row in fold]
		accuracy = accuracy_metric(actual, predicted)
		scores.append(accuracy)
	return scores	

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参考:

  1. csdn blog 随机森林
  2. csdn blog python实现随机森林;
  3. sklearn随机森林实现
  4. blog tuning random forest’s parameters
  5. csdn blog 随机森林python
  6. blog 随机森林声纳数据仿真
  7. GitHub决策树;
  8. kaggle random forest;
  9. 刘建平 scikit-learn随机森林调参小结;
    10.sklearn.ensemble.RandomForestClassifier ;

转载:https://blog.csdn.net/rosefun96/article/details/78833477
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