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Hold-out validation

As explained in Deep Learning with Python, Third Edition

An evaluation protocol that splits data once into separate subsets for training, validation, and/or testing.

Hold-out validation reserves part of a dataset, trains on the remainder, and evaluates on the reserved data. Keep a separate, untouched test set when tuning models. section 5.2.1

A simple split

Shuffle the data, set aside a validation slice, train on the remaining samples, and evaluate on the slice. After choosing the model, retrain with training and validation data combined, then measure generalization once on the untouched test set. section 5.2.1

Use these practical checks:

  • Treat unstable scores across different random splits as a warning that the validation or test sets are not representative. section 5.2.1
  • Prefer K-fold or iterated K-fold validation when limited data makes a single split unreliable. section 5.2.1

How Deep Learning with Python, Third Edition covers it

How deep it goes
Explains the split, training, evaluation, retraining, and small-data caveat, then defers repeated partitioning to K-fold methods.
Examples
Demonstrates shuffled array slicing, model fitting, validation evaluation, and final retraining with combined training and validation data.
What you can do after
Apply hold-out validation by splitting data, fitting a model, checking validation performance, and reserving test data for final evaluation.
How it connects
Connects training sets, validation sets, test sets, data leakage, K-fold cross-validation, and iterated K-fold validation.

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This explainer was generated by Manning's knowledge graph from the text of Deep Learning with Python, Third Edition. The section links point to the parts of the book it draws on.