sklearn之验证曲线

‘‘‘
    验证曲线：模型性能 = f(超参数)----通过优化模型参数，达到优化模型预测结果，使得模型预测更加精准
    验证曲线所需API：
            train_scores, test_scores = ms.validation_curve(
            model,        # 模型
            输入集, 输出集,
            ‘n_estimators‘,         #超参数名
            np.arange(50, 550, 50),    #超参数序列
            cv=5        #折叠数
            )

            train_scores的结构:
                超参数取值    第一次折叠    第二次折叠    第三次折叠    第四次折叠    第五次折叠
                        50    0.91823444    0.91968162    0.92619392    0.91244573    0.91040462
                        100    0.91968162    0.91823444    0.91244573    0.92619392    0.91244573
                        ...           ...            ...         ...            ...            ...
            test_scores的结构与train_scores的结构相同。

    案例：在小汽车评级案例中使用验证曲线选择较优参数。

‘‘‘

import numpy as np
import matplotlib.pyplot as mp
import sklearn.preprocessing as sp
import sklearn.ensemble as se
import sklearn.model_selection as ms
import sklearn.metrics as sm
import warnings

warnings.filterwarnings(‘ignore‘)

data = []
with open(‘./ml_data/car.txt‘, ‘r‘) as f:
    for line in f.readlines():
        sample = line[:-1].split(‘,‘)
        data.append(sample)
data = np.array(data)
# print(data.shape)

# 整理好每一列的标签编码器encoders
# 整理好训练输入集与输出集
data = data.T
# print(data.shape)
encoders = []
train_x, train_y = [], []
for row in range(len(data)):
    encoder = sp.LabelEncoder()
    if row < len(data) - 1:  # 不是最后列
        train_x.append(encoder.fit_transform(data[row]))
    else:  # 是最后一列，作为输出集
        train_y = encoder.fit_transform(data[row])
    encoders.append(encoder)

train_x = np.array(train_x).T
# 训练随机森林分类器
model = se.RandomForestClassifier(max_depth=6, n_estimators=150, random_state=7)

# 获取n_estimators的验证曲线
train_scores, test_scores = ms.validation_curve(model, train_x, train_y, ‘n_estimators‘, np.arange(50, 550, 50), cv=5)
# print(‘test_scores‘, test_scores, sep=‘\n‘)
# print(np.mean(test_scores, axis=1))

# 获取max_depth的验证曲线
train_scores1, test_scores1 = ms.validation_curve(model, train_x, train_y, ‘max_depth‘, np.arange(1, 7), cv=5)
# print(‘test_scores1‘, test_scores1, sep=‘\n‘)
# print(np.mean(test_scores1, axis=1))

# 训练之前进行交叉验证
cv = ms.cross_val_score(model, train_x, train_y, cv=4, scoring=‘f1_weighted‘)
# print(cv.mean())
model.fit(train_x, train_y)

# 自定义测试集，预测小汽车的等级
# 保证每个特征使用的标签编码器与训练时使用的标签编码器匹配
data = [
    [‘high‘, ‘med‘, ‘5more‘, ‘4‘, ‘big‘, ‘low‘, ‘unacc‘],
    [‘high‘, ‘high‘, ‘4‘, ‘4‘, ‘med‘, ‘med‘, ‘acc‘],
    [‘low‘, ‘low‘, ‘2‘, ‘4‘, ‘small‘, ‘high‘, ‘good‘],
    [‘low‘, ‘med‘, ‘3‘, ‘4‘, ‘med‘, ‘high‘, ‘vgood‘]]

data = np.array(data).T
test_x, test_y = [], []
for row in range(len(data)):
    encoder = encoders[row]  # 每列对应的标签编码器
    if row < len(data) - 1:
        test_x.append(encoder.transform(data[row]))  # 这里需要训练了，直接转换
    else:
        test_y = encoder.transform(data[row])
test_x = np.array(test_x).T

pred_test_y = model.predict(test_x)
print(pred_test_y)
pred_test_y = encoders[-1].inverse_transform(pred_test_y)
test_y = encoders[-1].inverse_transform(test_y)
# print(pred_test_y)
# print(test_y)

# 画图显示验证曲线
mp.figure(‘Validation Curve‘, facecolor=‘lightgray‘)
mp.subplot(211)
mp.title(‘N_estimators‘)
mp.xlabel(‘N_estimators‘)
mp.ylabel(‘f1 score‘)
mp.grid(linestyle=":")
mp.plot(np.arange(50, 550, 50), np.mean(test_scores, axis=1), label=‘N_estimators VC‘)
mp.legend()

mp.subplot(212)
mp.title(‘Max_depth‘)
mp.xlabel(‘Max_depth‘)
mp.ylabel(‘f1 score‘)
mp.grid(linestyle=":")
mp.plot(np.arange(1, 7), np.mean(test_scores1, axis=1), label=‘Max_depth VC‘)
mp.legend()

mp.show()



输出结果：

[2 0 0 3]
[‘unacc‘ ‘acc‘ ‘acc‘ ‘vgood‘]
[‘unacc‘ ‘acc‘ ‘good‘ ‘vgood‘]