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Can I use AdaBoost with random forest as a base classifier? I searched on the internet and I didn't find anyone who does it.

Like in the following code; I try to run it but it takes a lot of time:

estimators = Pipeline([('vectorizer', CountVectorizer()),
                       ('transformer', TfidfTransformer()),
                       ('classifier', AdaBoostClassifier(learning_rate=1))])

RF=RandomForestClassifier(criterion='entropy',n_estimators=100,max_depth=500,min_samples_split=100,max_leaf_nodes=None,
                          max_features='log2')


param_grid={
    'vectorizer__ngram_range': [(1,2),(1,3)],
    'vectorizer__min_df': [5],
    'vectorizer__max_df': [0.7],
    'vectorizer__max_features': [1500],

    'transformer__use_idf': [True , False],
    'transformer__norm': ('l1','l2'),
    'transformer__smooth_idf': [True , False],
     'transformer__sublinear_tf': [True , False],

    'classifier__base_estimator':[RF],
    'classifier__algorithm': ("SAMME.R","SAMME"),
    'classifier__n_estimators':[4,7,11,13,16,19,22,25,28,31,34,43,50]
}

I tried with the GridSearchCV, I added the RF classifier into the AdaBoost parameters. if I use it would the accuracy increase?

desertnaut
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3 Answers3

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Yes, Random Forest can be used as a base classifier of AdaBoost Classifier. Here is the link of one such model used in a research paper (https://www.researchgate.net/publication/339978251_A_Precise_Breast_Cancer_Detection_Approach_Using_Ensemble_of_Random_Forest_with_AdaBoost). In this paper authors have got improved accuracies than past literatures. If you search you will find some other research papers using similar type of models.

abhijeetsingh
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No wonder you have not actually seen anyone doing it - it is an absurd and bad idea.

You are trying to build an ensemble (Adaboost) which in itself consists of ensemble base classifiers (RFs) - essentially an "ensemble-squared"; so, no wonder about the high computation time.

But even if it was practical, there are good theoretical reasons not to do it; quoting from my own answer in Execution time of AdaBoost with SVM base classifier:

Adaboost (and similar ensemble methods) were conceived using decision trees as base classifiers (more specifically, decision stumps, i.e. DTs with a depth of only 1); there is good reason why still today, if you don't specify explicitly the base_classifier argument, it assumes a value of DecisionTreeClassifier(max_depth=1). DTs are suitable for such ensembling because they are essentially unstable classifiers, which is not the case with SVMs, hence the latter are not expected to offer much when used as base classifiers.

On top of this, SVMs are computationally much more expensive than decision trees (let alone decision stumps), which is the reason for the long processing times you have observed.

The argument holds for RFs, too - they are not unstable classifiers, hence there is not any reason to actually expect performance improvements when using them as base classifiers for boosting algorithms, like Adaboost.

desertnaut
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Short answer: It's not impossible. I don't know if there's anything wrong with doing so in theory, but I tried this once and the accuracy increased.

Long answer:

I tried it on a typical dataset with n rows of p real-valued features, and a label list of length n. In case it matters, they are embeddings of nodes in a graph obtained by the DeepWalk algorithm, and the nodes are categorized into two classes. I trained a few classification models on this data using 5-fold cross validation, and measured common evaluation metrics for them (precision, recall, AUC etc.). The models I have used are SVM, logistic regression, random Forest, 2-layer perceptron and Adaboost with random forest classifiers. The last model, Adaboost with random forest classifiers, yielded the best results (95% AUC compared to multilayer perceptron's 89% and random forest's 88%). Sure, now the runtime has increased by a factor of, let's say, 100, but it's still about 20 mins, so it's not a constraint to me.

Here's what I thought: Firstly, I'm using cross validation, so there's probably no overfitting flying under the radar. Secondly, both are ensemble learning methods, but random forest is a bagging method, wheras Adaboost is a boosting technique. Perhaps they're still different enough for their combination to make sense?

Esi
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