原理介紹

K折交叉驗證：

KFold，GroupKFold，StratifiedKFold，

留一法：

LeaveOneGroupOut，LeavePGroupsOut，LeaveOneOut，LeavePOut，

隨機劃分法：

ShuffleSplit，GroupShuffleSplit，StratifiedShuffleSplit，

代碼實現

流程：

實例化分類器 -> 叠代器叠代組[.split()]

KFold(n_splits=2)

#KFold
import numpy as np
from sklearn.model_selection import KFold
X=np.array([[1,2],[3,4],[5,6],[7,8],[9,10],[11,12]])
y=np.array([1,2,3,4,5,6])
kf=KFold(n_splits=2)    # 定義分成幾個組
# kf.get_n_splits(X)    # 查詢分成幾個組
print(kf)
for train_index,test_index in kf.split(X):
    print("Train Index:",train_index,",Test Index:",test_index)
    X_train,X_test=X[train_index],X[test_index]
    y_train,y_test=y[train_index],y[test_index]
    #print(X_train,X_test,y_train,y_test)

GroupKFold(n_splits=2)

# GroupKFold，不是很懂這個劃分方法
import numpy as np
from sklearn.model_selection import GroupKFold
X=np.array([[1,2],[3,4],[5,6],[7,8],[9,10],[11,12]])
y=np.array([1,2,3,4,5,6])
groups=np.array([1,2,3,4,5,6])
group_kfold=GroupKFold(n_splits=2)
group_kfold.get_n_splits(X,y,groups)
print(group_kfold)
for train_index,test_index in group_kfold.split(X,y,groups):
    print("Train Index:",train_index,",Test Index:",test_index)
    X_train,X_test=X[train_index],X[test_index]
    y_train,y_test=y[train_index],y[test_index]
    #print(X_train,X_test,y_train,y_test)

#GroupKFold(n_splits=2)
#Train Index: [0 2 4] ,Test Index: [1 3 5]
#Train Index: [1 3 5] ,Test Index: [0 2 4]

StratifiedKFold(n_splits=3)

# stratifiedKFold：保證訓練集中每一類的比例是相同的（盡量）
import numpy as np
from sklearn.model_selection import StratifiedKFold
X=np.array([[1,2],[3,4],[5,6],[7,8],[9,10],[11,12]])
y=np.array([1,1,1,2,2,2])
skf=StratifiedKFold(n_splits=3)
skf.get_n_splits(X,y)
print(skf)
for train_index,test_index in skf.split(X,y):
    print("Train Index:",train_index,",Test Index:",test_index)
    X_train,X_test=X[train_index],X[test_index]
    y_train,y_test=y[train_index],y[test_index]
    #print(X_train,X_test,y_train,y_test)

#StratifiedKFold(n_splits=3, random_state=None, shuffle=False)
#Train Index: [1 2 4 5] ,Test Index: [0 3]
#Train Index: [0 2 3 5] ,Test Index: [1 4]

LeaveOneOut()

# leaveOneOut：測試集就留下一個
import numpy as np
from sklearn.model_selection import LeaveOneOut
X=np.array([[1,2],[3,4],[5,6],[7,8],[9,10],[11,12]])
y=np.array([1,2,3,4,5,6])
loo=LeaveOneOut()
loo.get_n_splits(X)
print(loo)
for train_index,test_index in loo.split(X,y):
    print("Train Index:",train_index,",Test Index:",test_index)
    X_train,X_test=X[train_index],X[test_index]
    y_train,y_test=y[train_index],y[test_index]
    #print(X_train,X_test,y_train,y_test)
#LeaveOneOut()
#Train Index: [1 2 3 4 5] ,Test Index: [0]
#Train Index: [0 2 3 4 5] ,Test Index: [1]
#Train Index: [0 1 3 4 5] ,Test Index: [2]
#Train Index: [0 1 2 4 5] ,Test Index: [3]
#Train Index: [0 1 2 3 5] ,Test Index: [4]
#Train Index: [0 1 2 3 4] ,Test Index: [5]

LeavePOut(p=3)

LeavePOut：測試集留下P個
import numpy as np
from sklearn.model_selection import LeavePOut
X=np.array([[1,2],[3,4],[5,6],[7,8],[9,10],[11,12]])
y=np.array([1,2,3,4,5,6])
lpo=LeavePOut(p=3)
lpo.get_n_splits(X)
print(lpo)
for train_index,test_index in lpo.split(X,y):
    print("Train Index:",train_index,",Test Index:",test_index)
    X_train,X_test=X[train_index],X[test_index]
    y_train,y_test=y[train_index],y[test_index]
    #print(X_train,X_test,y_train,y_test)

#LeavePOut(p=3)
#Train Index: [3 4 5] ,Test Index: [0 1 2]
#Train Index: [2 4 5] ,Test Index: [0 1 3]
#Train Index: [2 3 5] ,Test Index: [0 1 4]
#Train Index: [2 3 4] ,Test Index: [0 1 5]
#Train Index: [1 4 5] ,Test Index: [0 2 3]
#Train Index: [1 3 5] ,Test Index: [0 2 4]
#Train Index: [1 3 4] ,Test Index: [0 2 5]
#Train Index: [1 2 5] ,Test Index: [0 3 4]
#Train Index: [1 2 4] ,Test Index: [0 3 5]
#Train Index: [1 2 3] ,Test Index: [0 4 5]
#Train Index: [0 4 5] ,Test Index: [1 2 3]
#Train Index: [0 3 5] ,Test Index: [1 2 4]
#Train Index: [0 3 4] ,Test Index: [1 2 5]
#Train Index: [0 2 5] ,Test Index: [1 3 4]
#Train Index: [0 2 4] ,Test Index: [1 3 5]
#Train Index: [0 2 3] ,Test Index: [1 4 5]
#Train Index: [0 1 5] ,Test Index: [2 3 4]
#Train Index: [0 1 4] ,Test Index: [2 3 5]
#Train Index: [0 1 3] ,Test Index: [2 4 5]
#Train Index: [0 1 2] ,Test Index: [3 4 5]

ShuffleSplit(n_splits=3,test_size=.25,random_state=0)

#ShuffleSplit 把數據集打亂順序，然後劃分測試集和訓練集，訓練集額和測試集的比例隨機選定，訓練集和測試集的比例的和可以小於1
 
import numpy as np
from sklearn.model_selection import ShuffleSplit
X=np.array([[1,2],[3,4],[5,6],[7,8],[9,10],[11,12]])
y=np.array([1,2,3,4,5,6])
rs=ShuffleSplit(n_splits=3,test_size=.25,random_state=0)
rs.get_n_splits(X)
print(rs)
for train_index,test_index in rs.split(X,y):
    print("Train Index:",train_index,",Test Index:",test_index)
    X_train,X_test=X[train_index],X[test_index]
    y_train,y_test=y[train_index],y[test_index]
    #print(X_train,X_test,y_train,y_test)
print("==============================")
rs=ShuffleSplit(n_splits=3,train_size=.5,test_size=.25,random_state=0)
rs.get_n_splits(X)
print(rs)
for train_index,test_index in rs.split(X,y):
    print("Train Index:",train_index,",Test Index:",test_index)

#ShuffleSplit(n_splits=3, random_state=0, test_size=0.25, train_size=None)
#Train Index: [1 3 0 4] ,Test Index: [5 2]
#Train Index: [4 0 2 5] ,Test Index: [1 3]
#Train Index: [1 2 4 0] ,Test Index: [3 5]
#==============================
#ShuffleSplit(n_splits=3, random_state=0, test_size=0.25, train_size=0.5)
#Train Index: [1 3 0] ,Test Index: [5 2]
#Train Index: [4 0 2] ,Test Index: [1 3]
#Train Index: [1 2 4] ,Test Index: [3 5]

StratifiedShuffleSplit(n_splits=3,test_size=.5,random_state=0)

# StratifiedShuffleSplitShuffleSplit 把數據集打亂順序，然後劃分測試集和訓練集，
# 訓練集額和測試集的比例隨機選定，訓練集和測試集的比例的和可以小於1,但是還要保證訓練集中各類所占的比例是一樣的

import numpy as np
from sklearn.model_selection import StratifiedShuffleSplit
X=np.array([[1,2],[3,4],[5,6],[7,8],[9,10],[11,12]])
y=np.array([1,2,1,2,1,2])
sss=StratifiedShuffleSplit(n_splits=3,test_size=.5,random_state=0)
sss.get_n_splits(X,y)
print(sss)
for train_index,test_index in sss.split(X,y):
    print("Train Index:",train_index,",Test Index:",test_index)
    X_train,X_test=X[train_index],X[test_index]
    y_train,y_test=y[train_index],y[test_index]
    #print(X_train,X_test,y_train,y_test)

#StratifiedShuffleSplit(n_splits=3, random_state=0, test_size=0.5,train_size=None)
#Train Index: [5 4 1] ,Test Index: [3 2 0]
#Train Index: [5 2 3] ,Test Index: [0 4 1]
#Train Index: [5 0 4] ,Test Index: [3 1 2]

『Sklearn』數據劃分方法