Add example script demonstrating preprocess() API usage

Co-authored-by: thinkall <3197038+thinkall@users.noreply.github.com>

Author: Copilot

notebook/preprocess_api_example.py

@@ -0,0 +1,96 @@
+"""
+Example demonstrating the use of FLAML's preprocess() API.
+
+This script shows how to use both task-level and estimator-level preprocessing
+APIs exposed by FLAML AutoML.
+"""
+
+from flaml import AutoML
+from sklearn.datasets import load_breast_cancer
+from sklearn.model_selection import train_test_split
+import numpy as np
+
+# Load and split data
+print("Loading breast cancer dataset...")
+X, y = load_breast_cancer(return_X_y=True)
+X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.2, random_state=42)
+
+print(f"Training data shape: {X_train.shape}")
+print(f"Test data shape: {X_test.shape}")
+
+# Train AutoML model
+print("\nTraining AutoML model...")
+automl = AutoML()
+automl_settings = {
+    "time_budget": 10,  # 10 seconds
+    "task": "classification",
+    "metric": "accuracy",
+    "estimator_list": ["lgbm", "xgboost"],
+    "verbose": 0,
+}
+automl.fit(X_train, y_train, **automl_settings)
+
+print(f"Best estimator: {automl.best_estimator}")
+print(f"Best accuracy: {1 - automl.best_loss:.4f}")
+
+# Example 1: Using task-level preprocessing
+print("\n" + "=" * 60)
+print("Example 1: Task-level preprocessing")
+print("=" * 60)
+X_test_task = automl.preprocess(X_test)
+print(f"Original test data shape: {X_test.shape}")
+print(f"After task preprocessing: {X_test_task.shape}")
+
+# Example 2: Using estimator-level preprocessing
+print("\n" + "=" * 60)
+print("Example 2: Estimator-level preprocessing")
+print("=" * 60)
+estimator = automl.model
+X_test_estimator = estimator.preprocess(X_test_task)
+print(f"After estimator preprocessing: {X_test_estimator.shape}")
+
+# Example 3: Complete preprocessing pipeline
+print("\n" + "=" * 60)
+print("Example 3: Complete preprocessing pipeline")
+print("=" * 60)
+# Apply both levels of preprocessing
+X_preprocessed = automl.preprocess(X_test)
+X_final = automl.model.preprocess(X_preprocessed)
+
+# Manual prediction using fully preprocessed data
+y_pred_manual = automl.model._model.predict(X_final)
+
+# Compare with AutoML's predict method (which does preprocessing internally)
+y_pred_auto = automl.predict(X_test)
+
+print(f"Predictions match: {np.array_equal(y_pred_manual, y_pred_auto)}")
+print(f"Manual prediction sample: {y_pred_manual[:5]}")
+print(f"Auto prediction sample: {y_pred_auto[:5]}")
+
+# Example 4: Using preprocessing for custom inference
+print("\n" + "=" * 60)
+print("Example 4: Custom inference with preprocessing")
+print("=" * 60)
+# You might want to apply preprocessing separately for:
+# - Debugging
+# - Custom inference pipelines
+# - Integration with other tools
+
+# Get preprocessed features
+X_features = automl.preprocess(X_test)
+X_features = automl.model.preprocess(X_features)
+
+# Now you can use these features with the underlying model or for analysis
+print(f"Preprocessed features ready for custom use: {X_features.shape}")
+print(f"Feature statistics - Mean: {np.mean(X_features):.4f}, Std: {np.std(X_features):.4f}")
+
+print("\n" + "=" * 60)
+print("Summary")
+print("=" * 60)
+print("The preprocess() API allows you to:")
+print("1. Apply task-level preprocessing with automl.preprocess()")
+print("2. Apply estimator-level preprocessing with estimator.preprocess()")
+print("3. Chain both for complete preprocessing pipeline")
+print("4. Use preprocessed data for custom inference or analysis")
+print("\nNote: Task-level preprocessing should always be applied before")
+print("      estimator-level preprocessing.")