如何将 GridsearchCV 与管道和多个分类器一起使用？

Question

我构建了一个modelPipeline，它运行多个分类器并将pipeline和每个分类器的分数作为DataFrame返回。

如何在下面的modelPipeline中使用GridsearchCV？是否可以在 Pipeline 中将GridsearchCV 与多个分类器一起使用？

from sklearn.linear_model import LogisticRegression
from sklearn.naive_bayes import BernoulliNB
from sklearn.neighbors import KNeighborsClassifier
from sklearn.svm import SVC
from sklearn.tree import DecisionTreeClassifier
from sklearn.ensemble import RandomForestClassifier, ExtraTreesClassifier
from sklearn.neural_network import MLPClassifier
from sklearn.pipeline import Pipeline
from xgboost import XGBClassifier
from sklearn.preprocessing import StandardScaler
from sklearn.model_selection import train_test_split
import sklearn.metrics as skm

import os
rs = {'random_state': 42}

# Train-test Split
X_train, X_test, y_train, y_test = train_test_split(X, 
                                                    y, 
                                                    test_size = 0.33, 
                                                    random_state = 42)

# Classification - Model Pipeline
def modelPipeline(X_train, X_test, y_train, y_test):

    log_reg = LogisticRegression(**rs)
    nb = BernoulliNB()
    knn = KNeighborsClassifier()
    svm = SVC(**rs)
    mlp = MLPClassifier(max_iter=500, **rs)
    dt = DecisionTreeClassifier(**rs)
    et = ExtraTreesClassifier(**rs)
    rf = RandomForestClassifier(**rs)
    xgb = XGBClassifier(**rs, verbosity=0)

    clfs = [
            ('Logistic Regression', log_reg), 
            ('Naive Bayes', nb),
            ('K-Nearest Neighbors', knn), 
            ('SVM', svm), 
            ('MLP', mlp), 
            ('Decision Tree', dt), 
            ('Extra Trees', et), 
            ('Random Forest', rf), 
            ('XGBoost', xgb)
            ]


    pipelines = []

    scores_df = pd.DataFrame(columns=['Model', 'F1_Score', 'Precision', 'Recall', 'Accuracy', 'ROC_AUC'])


    for clf_name, clf in clfs:

        pipeline = Pipeline(steps=[
                                   ('scaler', StandardScaler()),
                                   ('classifier', clf)
                                   ]
                            )
        pipeline.fit(X_train, y_train)


        y_pred = pipeline.predict(X_test)
        # F1-Score
        fscore = skm.f1_score(y_test, y_pred)
        # Precision
        pres = skm.precision_score(y_test, y_pred)
        # Recall
        rcall = skm.recall_score(y_test, y_pred)
        # Accuracy
        accu = skm.accuracy_score(y_test, y_pred)
        # ROC_AUC
        roc_auc = skm.roc_auc_score(y_test, y_pred)


        pipelines.append(pipeline)

        scores_df = scores_df.append({
                                      'Model' : clf_name, 
                                      'F1_Score' : fscore,
                                      'Precision' : pres,
                                      'Recall' : rcall,
                                      'Accuracy' : accu,
                                      'ROC_AUC' : roc_auc
                                      
                                      }, 
                                     ignore_index=True)
        
    return pipelines, scores_df

Answer 1

从您的 cmets 对我的另一个答案，也许您只是想调整每个模型？ （那么您应该将示例简化为单个分​​类器，因为多个分类器将独立运行（？）。）

所以，例如

    log_reg_params = {'C': [0.1, 1, 10]}
    ...
    xgb_params = {
        'learning_rate': [0.05, 0.1, 0.2],
        'max_depth': [1, 2, 3, 5, 8],
        'reg_lambda': [0, 1, 10],
    }

    clfs = [
        ('Logistic Regression', log_reg, log_reg_params), 
        ('Naive Bayes', nb, nb_params),
        ...
        ('XGBoost', xgb, xgb_params),
    ]
    for clf_name, clf, param_grid in clfs:
        pipeline = Pipeline(steps=[
            ('scaler', StandardScaler()),
            ('classifier', clf),
        ])
        search = GridSearchCV(pipeline, {f'classifier__{paramname}': paramvalue for paramname, paramvalue in param_grid.items()})
        search.fit(X_train, y_train)
        ...

Answer 2

GridSearchCV 可以得到一个分类器列表，供管道中的最后一步选择。但它不会完全按照您的代码执行：最值得注意的是，拟合模型不会被 GridSearchCV 保存，只是分数（以及最终选择的 refit-on-all-data 模型，如果 refit != False )。

pipe = Pipeline(steps=[
    ('scaler', StandardScaler()),
    ('classifier', DummyClassifier()),  # doesn't matter, we're going to override this in the search
])
params = {
    'classifier': [log_reg, nb, knn, svm, mlp, dt, et, rf, xgb],
}
scoring = ['f1', 'precision', 'recall', 'accuracy', 'roc_auc']
search = GridSearchCV(pipe, params, scoring=scoring, refit=False)

（多个指标需要将refit 设置为False、scoring 条目之一或自定义可调用项。）