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  3. Machine Learning with Tree-Based Models in Python
  • 1

    Classification and Regression Trees

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    Classification and Regression Trees (CART) are a set of supervised learning models used for problems involving classification and regression. In this chapter, you'll be introduced to the CART algorithm.

  • 2

    The Bias-Variance Tradeoff

    The bias-variance tradeoff is one of the fundamental concepts in supervised machine learning. In this chapter, you'll understand how to diagnose the problems of overfitting and underfitting. You'll also be introduced to the concept of ensembling where the predictions of several models are aggregated to produce predictions that are more robust.

  • 3

    Bagging and Random Forests

    Bagging is an ensemble method involving training the same algorithm many times using different subsets sampled from the training data. In this chapter, you'll understand how bagging can be used to create a tree ensemble. You'll also learn how the random forests algorithm can lead to further ensemble diversity through randomization at the level of each split in the trees forming the ensemble.

  • 4

    Boosting

    Boosting refers to an ensemble method in which several models are trained sequentially with each model learning from the errors of its predecessors. In this chapter, you'll be introduced to the two boosting methods of AdaBoost and Gradient Boosting.

  • 5

    Model Tuning

    The hyperparameters of a machine learning model are parameters that are not learned from data. They should be set prior to fitting the model to the training set. In this chapter, you'll learn how to tune the hyperparameters of a tree-based model using grid search cross validation.

Initializing

Exercise

Define the AdaBoost classifier

In the following exercises you'll revisit the Indian Liver Patient dataset which was introduced in a previous chapter. Your task is to predict whether a patient suffers from a liver disease using 10 features including Albumin, age and gender. However, this time, you'll be training an AdaBoost ensemble to perform the classification task. In addition, given that this dataset is imbalanced, you'll be using the ROC AUC score as a metric instead of accuracy.

As a first step, you'll start by instantiating an AdaBoost classifier.

Instructions

100 XP

  • Import AdaBoostClassifier from sklearn.ensemble.

  • Instantiate a DecisionTreeClassifier with max_depth set to 2.

  • Instantiate an AdaBoostClassifier consisting of 180 trees and setting the base_estimator to dt.