Python手写随机森林算法：从原理到泰坦尼克号实战

# -*- coding: utf-8 -*-
"""
@author: kim
"""
from model import *＃载入基分类器的代码
#ETL:same procedure to training set and test set
training=pd.read_csv('train.csv',index_col=0)
test=pd.read_csv('test.csv',index_col=0)
SexCode=pd.DataFrame([1,0],index=['female','male'],columns=['Sexcode']) ＃将性别转化为０１
training=training.join(SexCode,how='left',on=training.Sex)
training=training.drop(['Name','Ticket','Embarked','Cabin','Sex'],axis=1)＃删去几个不参与建模的变量，包括姓名、船票号，船舱号
test=test.join(SexCode,how='left',on=test.Sex)
test=test.drop(['Name','Ticket','Embarked','Cabin','Sex'],axis=1)
print('ETL IS DONE!')
#MODEL FITTING
#===============PARAMETER AJUSTMENT============
min_leaf=1
min_dec_gini=0.0001
n_trees=5
n_fea=int(math.sqrt(len(training.columns)-1))
#==============================================
'''''
BEST SCORE:0.83
min_leaf=30
min_dec_gini=0.001
n_trees=20
'''
#ESSEMBLE BY RANDOM FOREST
FOREST={}
tmp=list(training.columns)
tmp.pop(tmp.index('Survived'))
feaList=pd.Series(tmp)
for t in range(n_trees):
#  fea=[]
  feasample=feaList.sample(n=n_fea,replace=False)#select feature
  fea=feasample.tolist()
  fea.append('Survived')
#    feaNew=fea.append(target)
  subset=training.sample(n=len(training),replace=True)#generate the dataset with replacement
  subset=subset[fea]
#  print(str(t)+' Classifier built on feature:')
#  print(list(fea))
  FOREST[t]=tree_grow(subset,'Survived',min_leaf,min_dec_gini) #save the tree
#MODEL PREDICTION
#======================
currentdata=training
output='submission_rf_20151116_30_0.001_20'
#======================
prediction={}
for r in currentdata.index:#a row
  prediction_vote={1:0,0:0}
  row=currentdata.get(currentdata.index==r)
  for n in range(n_trees):
    tree_dict=FOREST[n] #a tree
    p=model_prediction(tree_dict,row)
    prediction_vote[p]+=1
  vote=pd.Series(prediction_vote)
  prediction[r]=list(vote.order(ascending=False).index)[0]#the vote result
result=pd.Series(prediction,name='Survived_p')
#del prediction_vote
#del prediction
#result.to_csv(output)
t=training.join(result,how='left')
accuracy=round(len(t[t['Survived']==t['Survived_p']])/len(t),5)
print(accuracy)

# -*- coding: utf-8 -*-
"""
@author: kim
"""
import pandas as pd
import numpy as np
#import sklearn as sk
import math
def tree_grow(dataframe,target,min_leaf,min_dec_gini):
  tree={} #renew a tree
  is_not_leaf=(len(dataframe)>min_leaf)
  if is_not_leaf:
    fea,sp,gd=best_split_col(dataframe,target)
    if gd>min_dec_gini:
      tree['fea']=fea
      tree['val']=sp
#      dataframe.drop(fea,axis=1) #1116 modified
      l,r=dataSplit(dataframe,fea,sp)
      l.drop(fea,axis=1)
      r.drop(fea,axis=1)
      tree['left']=tree_grow(l,target,min_leaf,min_dec_gini)
      tree['right']=tree_grow(r,target,min_leaf,min_dec_gini)
    else:#return a leaf
      return leaf(dataframe[target])
  else:
    return leaf(dataframe[target])
  return tree
def leaf(class_lable):
  tmp={}
  for i in class_lable:
    if i in tmp:
      tmp[i]+=1
    else:
      tmp[i]=1
  s=pd.Series(tmp)
  s.sort(ascending=False)
  return s.index[0]
def gini_cal(class_lable):
  p_1=sum(class_lable)/len(class_lable)
  p_0=1-p_1
  gini=1-(pow(p_0,2)+pow(p_1,2))
  return gini
def dataSplit(dataframe,split_fea,split_val):
  left_node=dataframe[dataframe[split_fea]<=split_val]
  right_node=dataframe[dataframe[split_fea]>split_val]
  return left_node,right_node
def best_split_col(dataframe,target_name):
  best_fea=''#modified 1116
  best_split_point=0
  col_list=list(dataframe.columns)
  col_list.remove(target_name)
  gini_0=gini_cal(dataframe[target_name])
  n=len(dataframe)
  gini_dec=-99999999
  for col in col_list:
    node=dataframe[[col,target_name]]
    unique=node.groupby(col).count().index
    for split_point in unique: #unique value
      left_node,right_node=dataSplit(node,col,split_point)
      if len(left_node)>0 and len(right_node)>0:
        gini_col=gini_cal(left_node[target_name])*(len(left_node)/n)+gini_cal(right_node[target_name])*(len(right_node)/n)
        if (gini_0-gini_col)>gini_dec:
          gini_dec=gini_0-gini_col#decrease of impurity
          best_fea=col
          best_split_point=split_point
    #print(col,split_point,gini_0-gini_col)
  return best_fea,best_split_point,gini_dec
def model_prediction(model,row): #row is a df
  fea=model['fea']
  val=model['val']
  left=model['left']
  right=model['right']
  if row[fea].tolist()[0]<=val:#get the value
    branch=left
  else:
    branch=right
  if ('dict' in str( type(branch) )):
    prediction=model_prediction(branch,row)
  else:
    prediction=branch
  return prediction