Machine Learning Lecture 12: Ensemble Learning
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Questions and Answers

What is a Random Forest?

  • Bagging with trees + random feature subsets (correct)
  • A single decision tree
  • Boosting with trees
  • Stacking with multiple models
  • Random Forest can only be used for classification problems.

    False

    What is the main idea behind Stacking?

    Combining multiple classification models via a meta-classifier.

    The default criterion for sklearn.ensemble.RandomForestClassifier is _______________.

    <p>gini</p> Signup and view all the answers

    What is the purpose of the meta-classifier in Stacking?

    <p>To combine the outputs of individual models</p> Signup and view all the answers

    StackingCVClassifier uses pre-fitted classifiers.

    <p>True</p> Signup and view all the answers

    What is the difference between RandomForestClassifier and RandomForestRegressor?

    <p>One is for classification and the other is for regression.</p> Signup and view all the answers

    In Random Forest, max_features is set to _______________ by default.

    <p>'sqrt'</p> Signup and view all the answers

    Match the following ensemble learning techniques with their descriptions:

    <p>Random Forest = Combining multiple decision trees with random feature subsets Stacking = Combining multiple models via a meta-classifier Bagging = Bootstrapping and aggregating multiple models</p> Signup and view all the answers

    Stacking can only be used with models that operate on the same feature subsets.

    <p>False</p> Signup and view all the answers

    Study Notes

    Ensemble Learning

    • Ensemble learning is a method of combining multiple base models to create a stronger predictive model.

    Voting

    • Majority voting is a type of ensemble learning where multiple independent classifiers are combined to make a prediction.
    • The error rate of the ensemble is computed using a binomial probability distribution.
    • The probability of a wrong prediction by the ensemble is calculated based on the number of classifiers making a wrong prediction.
    • Soft voting is a type of voting where classifiers are assigned weights based on their performance.

    Bagging (Bootstrap Aggregating)

    • Bagging is an ensemble learning technique that combines multiple instances of the same base model, each trained on a random subset of the training data.
    • Bootstrap sampling is used to create the random subsets of the training data.

    Boosting

    • Boosting is an ensemble learning technique that combines multiple weak learners to create a strong learner.
    • In general boosting, each subsequent model is trained on the mistakes of the previous model.
    • AdaBoost is a type of boosting that uses a weighted training dataset to focus on the mistakes of the previous model.

    Gradient Boosting

    • Gradient boosting is a type of boosting that combines multiple weak learners to create a strong learner.
    • Trees are fit sequentially to improve the error of the previous trees.
    • The trees are combined using an additive approach.

    Random Forest

    • Random Forest is an ensemble learning technique that combines bagging with trees and random feature subsets.
    • The algorithm combines multiple decision trees, each trained on a random subset of the training data and a random subset of features.
    • Random Forest can be used for both classification and regression tasks.

    Stacking

    • Stacking is an ensemble learning technique that combines multiple classification models using a meta-classifier.
    • The individual classification models are trained on the complete training set, and then the meta-classifier is fitted based on the outputs of the individual models.
    • The meta-classifier can be trained on either the predicted class labels or probabilities from the individual models.

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    Description

    This quiz covers the concepts of ensemble learning, including majority voting and error rates, as part of a machine learning course.

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