python使用k折交叉验证的代码
K折交叉验证:sklearn.model_selection.KFold(n_splits=3, shuffle=False, random_state=None)
思路:将训练/测试数据集划分n_splits个互斥子集,每次用其中一个子集当作验证集,剩下的n_splits-1个作为训练集,进行n_splits次训练和测试,得到n_splits个结果
注意点:对于不能均等份的数据集,其前n_samples % n_splits子集拥有n_samples // n_splits + 1个样本,其余子集都只有n_samples // n_splits样本
参数说明:
n_splits:表示划分几等份
shuffle:在每次划分时,是否进行洗牌
①若为Falses时,其效果等同于random_state等于整数,每次划分的结果相同
②若为True时,每次划分的结果都不一样,表示经过洗牌,随机取样的
random_state:随机种子数
属性:
①get_n_splits(X=None, y=None, groups=None):获取参数n_splits的值
②split(X, y=None, groups=None):将数据集划分成训练集和测试集,返回索引生成器
通过一个不能均等划分的栗子,设置不同参数值,观察其结果
①设置shuffle=False,运行两次,发现两次结果相同
import numpy as np
from sklearn.model_selection import KFold
x = np.array([[1, 2], [ 3, 4], [ 1, 2], [3, 4]])
y = np.array([, , , ])
kf = KFold(n_splits=)
k = kf.get_n_splits(x)
print(kf)
for train_index, test_index in kf.split(x): #几折循环几次,相应得到几次结果,这里参数写Y也一样
print('TRAIN:', train_index, "TEST:", kf.split(x))
x_train, x_test = x[train_index], x[test_index]
y_train, y_test = y[train_index], y[test_index]
See also
- StratifiedKFold
Takes group information into account to avoid building folds with imbalanced class distributions (for binary or multiclass classification tasks).
- GroupKFold
K-fold iterator variant with non-overlapping groups.
- RepeatedKFold
Repeats K-Fold n times.