GridSearch on Model and Classifiers

Question

I just came across this example on Model Grid Selection here:

https://chrisalbon.com/machine_learning/model_selection/model_selection_using_grid_search/

Question

Answer 1

Pipeline is used to chain sequential data transformation models followed last by the classifier / regressor. Something like first converting the text to numbers using TfidfVectorizer and then training the classifier.

pipe = Pipeline([('vectorizer',TfidfVectorizer()), 
                 ('classifier', RandomForestClassifier())])

For only a single class, no need of Pipeline.

Here in your code, its used as a placeholder, so that the parameters can be used by using the 'classifier' prefix. And the classifier itself can be substituted from the params.