#特征工程
#1-1sklearn中进行特征选择
#筛选法-方差筛选过滤
import numpy as np
import array
from sklearn.feature_selection import VarianceThreshold
x=[[0,0,1],[0,1,0],[1,0,0],[0,1,1],[0,1,0],[0,1,1]]
sel=VarianceThreshold(threshold=(.8*(1-.8))) #第一列0的比例超过了80%,在结果里剔除这一个特征
print(sel.fit_transform(x))
#卡方检验s筛选2个最好的特征
from sklearn.datasets import load_iris
from sklearn.feature_selection import SelectKBest
from sklearn.feature_selection import chi2
from scipy.stats import pearsonr
iris=load_iris()
x,y=iris.data,iris.target
print(x.shape)
x_new=SelectKBest(chi2,k=2).fit_transform(x,y)
print(x_new.shape)
print(np.hstack([x,x_new]))
'''
#使用相关系数的方法进行特征选择
#x_new=SelectKBest(lambda X, Y: array(map(lambda x: pearsonr(x, Y),X.T)).T, k=2).fit_transform(x,y)
#print(x_new.shape)
#print(np.hstack([x,x_new]))
#基于互信息法来进行相关性的判断
from sklearn.feature_selection import SelectKBest
from minepy import MINE
# 由于MINE的设计不是函数式的，定义mic方法将其为函数式的，返回一个二元组，二元组的第2项设置成固定的P值0.5
def mic(x, y):
m = MINE()
m.compute_score(x, y)
return (m.mic(), 0.5)
# 选择K个最好的特征，返回特征选择后的数据
SelectKBest(lambda X, Y: array(map(lambda x: mic(x, Y), X.T)).T, k=2).fit_transform(iris.data, iris.target)
'''
#包装法-根据模型选择特征-递归特性消除法
#选定一些算法，根据算法在数量上的表现来进行特征集合，一般选择用的算法包括随机森林，支持向量机和k近邻算法
import matplotlib.pyplot as plt
from sklearn.svm import SVC
from sklearn.model_selection import StratifiedKFold
from sklearn.feature_selection import RFECV
from sklearn.datasets import make_classification
#创建一个虚拟分类数据集1000个样本，8个分类结果，25个特征
x,y=make_classification(n_samples=1000,n_features=25,n_informative=3,n_redundant=2,
n_repeated=0,n_classes=8,n_clusters_per_class=1,random_state=0)
svc=SVC(kernel="linear")
rfec=RFECV(estimator=svc,step=1,cv=StratifiedKFold(2),scoring="accuracy")
rfec.fit(x,y)
print("Optimal number of features: %d" % rfec.n_features_)
print(rfec.ranking_) #输出各个特征重要性序号，选择的特征是1，其他依次排序
print(rfec.support_)
plt.figure()
plt.xlabel("number of features selected")
plt.ylabel("Cross validation score(nb of correct classificaions)")
plt.plot(range(1,len(rfec.grid_scores_)+1),rfec.grid_scores_)
plt.ylim([0,1])
plt.show()
#嵌入法-基于惩罚项的特征选择方法-很少用这个方法
from sklearn.svm import LinearSVC
from sklearn.datasets import load_iris
from sklearn.feature_selection import SelectFromModel
iris=load_iris()
x,y=iris.data,iris.target
print("原来数据的特征维度为：",x.shape)
lsvc=LinearSVC(C=0.01,penalty="l1",dual=False)
lsvc.fit(x,y)
model=SelectFromModel(lsvc,prefit=True)
x_new=model.transform(x)
print("l1惩罚项处理之后的数据维度为：",x_new.shape)
#嵌入法之基于树模型的特征选择法
from sklearn.ensemble import ExtraTreesClassifier
from sklearn.datasets import load_iris
x,y=iris.data,iris.target
print("原来数据的特征维度为：",x.shape)
clf=ExtraTreesClassifier()
clf.fit(x,y)
print(clf.feature_importances_)
model=SelectFromModel(clf,prefit=True)
x_new=model.transform(x)
print("新数据维度为：",x_new.shape)
#1-2特征变换与特征提取
#ong-hot的两种方法
from sklearn.preprocessing import OneHotEncoder
from sklearn.datasets import load_iris
iris=load_iris()
print(OneHotEncoder().fit_transform(iris.target.reshape(-1,1)).toarray())
#pandas中的one-hot方法
import pandas as pd
print(pd.get_dummies(iris.target))
#特征组合和降维：主要是从业务的层面进行考虑,在单特征不能取得进一步效果时，需要对于各个原生的单特征进行进行计算组合出新的特征，特别需要业务考量，而不是随意组合
#2 招聘数据的特征工程探索
import warnings
warnings.filterwarnings("ignore")
import numpy as np
import pandas as pd
#导入数据
la=pd.read_csv("D:Byrbt2018StudyPython机器学习全流程项目实战精讲配套课件第六讲 特征工程lagou_data5.csv",encoding="gbk")
print(la.head())
#advantage和label这两个特征作用不大，可以在最后剔除掉
#分类变量one-hot处理
#pandas ona-hot方法
print(pd.get_dummies(la["city"].head()))
'''
#sklearn方法
#先将文本信息进行分列编码
from sklearn.preprocessing import OneHotEncoder
from sklearn.preprocessing import LabelEncoder
la1=LabelEncoder()
la1.fit(list(la["city"].values))
la["city"]=la1.transform(list(la["city"].values))
print(la["city"].head())
#再由硬编码转变为one-hot编码
df=OneHotEncoder().fit_transform(la["city"].values.reshape(-1,1)).toarray()
print(df[:5])
'''
#对于招聘数据特征分类变量进行逐个的one-hot处理
f=["city","industry","education","position_name","size","stage","work_year"]
for i in f:
temp=pd.get_dummies(la[i])
la=pd.concat([la,temp],axis=1) #将转换的列合并
la=la.drop([i],axis=1) #删掉之前的变量
print(la.shape)
#删掉原来的特征即可
pd.options.display.max_columns=99
la=la.drop(["advantage","label","position_detail","salary"],axis=1)
print(la.shape)
print(la.head())
la1=la
#文本类信息的特征提取方法Python-Java-Excel-SQL-R等特征有误分类列
la=pd.read_csv("D:Byrbt2018StudyPython机器学习全流程项目实战精讲配套课件第六讲 特征工程lagou_data5.csv",encoding="gbk")
la=la[["position_detail","salary"]]
#提取python信息的特征列
for i,j in enumerate(la["position_detail"]):
if "python" in j:
la["position_detail"][i]=j.replace("python","Python")
la["Python"]=pd.Series()
for i, j in enumerate(la["position_detail"]):
if "Python" in j:
la["Python"][i] =1
else:
la["Python"][i] =0
print(la["Python"].head())
la["R"]=pd.Series()
for i, j in enumerate(la["position_detail"]):
if "R" in j:
la["R"][i] =1
else:
la["R"][i] =0
print(la["R"].value_counts())
for i,j in enumerate(la["position_detail"]):
if "sql" in j:
la["position_detail"][i]=j.replace("sql","SQL")
la["SQL"]=pd.Series()
for i, j in enumerate(la["position_detail"]):
if "SQL" in j:
la["SQL"][i] =1
else:
la["SQL"][i] =0
print(la["SQL"].value_counts())
la["Excel"]=pd.Series()
for i, j in enumerate(la["position_detail"]):
if "Excel" in j:
la["Excel"][i] =1
else:
la["Excel"][i] =0
print(la["Excel"].value_counts())
la["Java"]=pd.Series()
for i, j in enumerate(la["position_detail"]):
if "Java" in j:
la["Java"][i] =1
else:
la["Java"][i] =0
print(la["Java"].value_counts())
for i,j in enumerate(la["position_detail"]):
if "linux" in j:
la["position_detail"][i]=j.replace("linux","Linux")
la["Linux"]=pd.Series()
for i, j in enumerate(la["position_detail"]):
if "Linux" in j:
la["Linux"][i] =1
else:
la["Linux"][i] =0
print(la["Linux"].value_counts())
la["C++"]=pd.Series()
for i, j in enumerate(la["position_detail"]):
if "C++" in j:
la["C++"][i] =1
else:
la["C++"][i] =0
print(la["C++"].value_counts())
for i,j in enumerate(la["position_detail"]):
if "spark" in j:
la["position_detail"][i]=j.replace("spark","Spark")
la["Spark"]=pd.Series()
for i, j in enumerate(la["position_detail"]):
if "Spark" in j:
la["Spark"][i] =1
else:
la["Spark"][i] =0
print(la["Spark"].value_counts())
for i,j in enumerate(la["position_detail"]):
if "tensorflow" in j:
la["position_detail"][i]=j.replace("tensorflow","Tensorflow")
if "TensorFlow" in j:
la["position_detail"][i]=j.replace("TensorFlow","Tensorflow")
la["Tensorflow"]=pd.Series()
for i, j in enumerate(la["position_detail"]):
if "Tensorflow" in j:
la["Tensorflow"][i] =1
else:
la["Tensorflow"][i] =0
print(la["Tensorflow"].value_counts())
la=la.drop(["position_detail"],axis=1)
print(la.head())
la=pd.concat((la,la1),axis=1).reset_index(drop=True)
print(la.head())
print(la.shape)