Metodi di scikit-learn

Hai deciso di creare un modello di regressione per prevedere il numero di nuovi dipendenti che la tua azienda assumerà con successo il prossimo mese. Apri un nuovo script Python per iniziare, ma ti rendi subito conto che sklearn ha un bel po’ di moduli diversi. Assicuriamoci che tu conosca i nomi dei moduli, i metodi e in quale modulo si trovi ciascun metodo.

Segui le istruzioni qui sotto per importare tutti i metodi necessari a eseguire la cross-validation con sklearn. Userai i moduli:

metrics
model_selection
ensemble

Questo esercizio fa parte del corso

Validazione dei modelli in Python

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Istruzioni dell'esercizio

Importa il metodo per calcolare gli score della cross-validation.
Importa il metodo della random forest per la regressione.
Importa la metrica mean square error.
Importa il metodo per creare uno scorer da usare con la cross-validation.

Esercizio pratico interattivo

Prova a risolvere questo esercizio completando il codice di esempio.

# Instruction 1: Load the cross-validation method
from sklearn.____ import ____

# Instruction 2: Load the random forest regression model
from sklearn.____ import ____

# Instruction 3: Load the mean squared error method
# Instruction 4: Load the function for creating a scorer
from sklearn.metrics import ____, ____

Modifica ed esegui il codice

Questo esercizio fa parte del corso

Validazione dei modelli 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: I limiti dei set di holdout Exercise 2: Due campioni Exercise 3: Problemi potenziali Exercise 4: Validazione incrociata Exercise 5: `KFold()` di scikit-learn Exercise 6: Utilizzare gli indici di KFold Exercise 7: cross_val_score() di sklearn Exercise 8: Metodi di scikit-learn

Esercizio in corso

Exercise 9: Usa cross_val_score()Exercise 10: Leave-one-out cross-validation (LOOCV)Exercise 11: Quando usare 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!