超参数调优进阶：Optuna/Bayesian/Early Stopping

1. 调优方法对比

超参数调优方法： ├── 网格搜索（Grid Search）：穷举所有组合，慢但全面 ├── 随机搜索（Random Search）：随机采样，快但不保证最优 ├── 贝叶斯优化（Bayesian）：基于历史结果智能搜索 └── 早停法（Early Stopping）：训练中动态停止

2. Optuna 调优

importoptunafromsklearn.ensembleimportRandomForestClassifierfromsklearn.model_selectionimportcross_val_scoredefobjective(trial):params={'n_estimators':trial.suggest_int('n_estimators',50,300),'max_depth':trial.suggest_int('max_depth',3,15),'min_samples_split':trial.suggest_int('min_samples_split',2,20),'min_samples_leaf':trial.suggest_int('min_samples_leaf',1,10),'max_features':trial.suggest_categorical('max_features',['sqrt','log2',None]),}model=RandomForestClassifier(**params,random_state=42)scores=cross_val_score(model,X_train,y_train,cv=5,scoring='accuracy')returnscores.mean()study=optuna.create_study(direction='maximize')study.optimize(objective,n_trials=100,show_progress_bar=True)print(f"最佳参数:{study.best_params}")print(f"最佳分数:{study.best_value:.4f}")

3. XGBoost + Optuna

importoptunaimportxgboostasxgbdefobjective_xgb(trial):params={'n_estimators':trial.suggest_int('n_estimators',50,500),'max_depth':trial.suggest_int('max_depth',3,12),'learning_rate':trial.suggest_float('learning_rate',0.01,0.3,log=True),'subsample':trial.suggest_float('subsample',0.6,1.0),'colsample_bytree':trial.suggest_float('colsample_bytree',0.6,1.0),'reg_alpha':trial.suggest_float('reg_alpha',1e-8,10.0,log=True),'reg_lambda':trial.suggest_float('reg_lambda',1e-8,10.0,log=True),}model=xgb.XGBClassifier(**params,random_state=42,use_label_encoder=False)scores=cross_val_score(model,X_train,y_train,cv=5,scoring='accuracy')returnscores.mean()study=optuna.create_study(direction='maximize')study.optimize(objective_xgb,n_trials=200)

4. Early Stopping

importlightgbmaslgb train_data=lgb.Dataset(X_train,label=y_train)val_data=lgb.Dataset(X_val,label=y_val,reference=train_data)params={'objective':'binary','metric':'binary_logloss','learning_rate':0.05,'num_leaves':31,}callbacks=[lgb.early_stopping(stopping_rounds=50),lgb.log_evaluation(period=10),]model=lgb.train(params,train_data,valid_sets=[val_data],num_boost_round=1000,callbacks=callbacks,)

总结