Cross-validation

Introduction

Cross-validation — Rotate train/validation folds for stable estimates. This lesson pairs the idea with a minimal Python/sklearn workflow you can extend in a notebook.

Understanding the topic

Concept Rotate train/validation folds for stable estimates.

Workflow Load data → preprocess → fit or apply technique → measure on hold-out data.

In practice Start with a small public dataset before jumping to proprietary production data.

• Concept — Rotate train/validation folds for stable estimates.
• Workflow — Load data → preprocess → fit or apply technique → measure on hold-out data.
• In practice — Start with a small public dataset before jumping to proprietary production data.

Step-by-step explanation

1. Concept — Rotate train/validation folds for stable estimates.
2. Workflow — Load data → preprocess → fit or apply technique → measure on hold-out data.
3. In practice — Start with a small public dataset before jumping to proprietary production data.

Informative example

Python starter:

# Cross-validation — starter sketch
print("Topic: Cross-validation")

Topic: Cross-validation

Execution workflow

Best practices

• Hold out a test set before hyperparameter tuning.
• Scale numeric columns for distance-based models.
• Track multiple metrics — not accuracy alone on skewed labels.

Common mistakes

• Leaking test statistics into preprocessing fit on full data.
• Training on the same rows you report as test performance.
• Chasing complex models before a simple baseline.

Hands-on exercise

Practice:

• Apply Cross-validation on a sample dataset
• Write down one metric that proves the technique helped

Summary

Cross-validation: Rotate train/validation folds for stable estimates.