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End to End ML Project - Fine tune your model with Cross Validation

In this step we will fine tune our models using cross validation. It is a resampling technique that is used to evaluate machine learning models on a limited data sample.

A test set should still be kept aside for final evaluation. We would no longer need a validation set (which is sometimes called the dev set) while doing cross validation. The training set is split into k smaller sets (there are other approaches too, but they generally follow the same principles). The following procedure is followed for each of the k folds:

  • A model is trained using k-1 of the folds as training data
  • The resulting model is validated on the remaining part of the data (i.e., it is used as a test set to compute a performance measure such as accuracy)
  • The performance measure reported by k-fold cross-validation is then the average of the values computed in the loop.

Given below is a visual representation of this process:

enter image description here

This image is from the official page of the Scikit-learn cross validation where you can find more details about the process.

Now let's work on fine tuning our models using cross validation.

INSTRUCTIONS
  • First, let's define a function called display_scores that would display the scores, mean, and standard deviation of all the models after applying cross validation

    def <<your code goes here>>(scores):
        print("Scores:", scores)
        print("Mean:", scores.mean())
        print("Standard deviation:", scores.std())
    
  • Now let's import cross_val_score from Scikit-learn

    from sklearn.model_selection import <<your code goes here>>
    
  • Now let's calculate the cross validation scores for our Decision Tree model

    scores = cross_val_score(tree_reg, housing_prepared, housing_labels,
                             scoring="neg_mean_squared_error", cv=10)
    tree_rmse_scores = np.sqrt(-scores)
    display_scores(tree_rmse_scores)
    
  • Finally, let's calculate the cross validation scores for our Random Forest model

    forest_scores = cross_val_score(forest_reg, housing_prepared, housing_labels,
                                    scoring="neg_mean_squared_error", cv=10)
    forest_rmse_scores = np.sqrt(-forest_scores)
    display_scores(forest_rmse_scores)
    

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