Twee steekproeven

Na het bouwen van meerdere classificatiemodellen op basis van de tic_tac_toe-gegevensset merk je dat sommige modellen minder goed generaliseren dan andere. Je hebt trainings- en test-splits gemaakt zoals je hebt geleerd, dus je vraagt je af waarom je validatieproces niet werkt.

Na een andere train-test-split te proberen, zag je verschillende accuracies voor je Machine Learning-model. Voordat je je te veel ergert aan de wisselende resultaten, besluit je te onderzoeken wat er nog meer aan de hand kan zijn.

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Modelvalidatie in Python

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# Create two different samples of 200 observations 
sample1 = tic_tac_toe.____(____, random_state=1111)
sample2 = tic_tac_toe.____(____, random_state=1171)

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Modelvalidatie in Python

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Before we can validate models, we need an understanding of how to create and work with them. This chapter provides an introduction to running regression and classification models in scikit-learn. We will use this model building foundation throughout the remaining chapters.

Exercise 1: Introduction to model validation Exercise 2: Modeling steps Exercise 3: Seen vs. unseen data Exercise 4: Regression models Exercise 5: Set parameters and fit a model Exercise 6: Feature importances Exercise 7: Classification models Exercise 8: Classification predictions Exercise 9: Reusing model parameters Exercise 10: Random forest classifier

This chapter focuses on the basics of model validation. From splitting data into training, validation, and testing datasets, to creating an understanding of the bias-variance tradeoff, we build the foundation for the techniques of K-Fold and Leave-One-Out validation practiced in chapter three.

Exercise 1: Creating train, test, and validation datasets Exercise 2: Create one holdout set Exercise 3: Create two holdout sets Exercise 4: Why use holdout sets Exercise 5: Accuracy metrics: regression models Exercise 6: Mean absolute error Exercise 7: Mean squared error Exercise 8: Performance on data subsets Exercise 9: Classification metrics Exercise 10: Confusion matrices Exercise 11: Confusion matrices, again Exercise 12: Precision vs. recall Exercise 13: The bias-variance tradeoff Exercise 14: Error due to under/over-fitting Exercise 15: Am I underfitting?

Holdout sets are a great start to model validation. However, using a single train and test set if often not enough. Cross-validation is considered the gold standard when it comes to validating model performance and is almost always used when tuning model hyper-parameters. This chapter focuses on performing cross-validation to validate model performance.

Exercise 1: De problemen met holdout-sets Exercise 2: Twee steekproeven

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Exercise 3: Mogelijke problemen Exercise 4: Cross-validatie Exercise 5: scikit-learn's KFold()Exercise 6: KFold-indices gebruiken Exercise 7: sklearns cross_val_score()Exercise 8: Methode’s van scikit-learn Exercise 9: Implementeer cross_val_score()Exercise 10: Leave-one-out-cross-validation (LOOCV)Exercise 11: Wanneer gebruik je LOOCV Exercise 12: Leave-one-out-cross-validation

The first three chapters focused on model validation techniques. In chapter 4 we apply these techniques, specifically cross-validation, while learning about hyperparameter tuning. After all, model validation makes tuning possible and helps us select the overall best model.

Exercise 1: Introduction to hyperparameter tuning Exercise 2: Creating Hyperparameters Exercise 3: Running a model using ranges Exercise 4: RandomizedSearchCV Exercise 5: Preparing for RandomizedSearch Exercise 6: Implementing RandomizedSearchCV Exercise 7: Selecting your final model Exercise 8: Best classification accuracy Exercise 9: Selecting the best precision model Exercise 10: Course completed!