Clarification on MultiClassClassifier

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Clarification on MultiClassClassifier

fpetrulio
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Re: Clarification on MultiClassClassifier

Eibe Frank-2
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Yes, the MultiClassClassifier turns a multi-class problem into several binary-class problems. By default, it uses the one-vs-rest method. However, it can also optionally

(a) perform one-vs-one (aka pairwise) classification (and, with a further option turned on, pairwise coupling), or

(b) use random error-correcting output codes, or

(c) use exhaustive error-correcting output codes.

In each case, binary classification problems are created. You can look at the classifiers that are generated in the output (assuming the base classifier is a decision tree or something that has  a nice printable representation).

Cheers,
Eibe

> On 8/06/2021, at 12:40 AM, [hidden email] wrote:
>
> Hi,
> looking at the documentation [https://www.cs.waikato.ac.nz/ml/weka/Witten_et_al_2016_appendix.pdf] it seems that whenever a MultiClassClassifier is used, the multi-class problem is treated as a binary one (I guess comparing one class vs the rest). However, there is no reference on how the problem is handled without toning the base classifier. To be clear:
> 1. if I use i.e. a Random Forest or J48 classifiers for multiclass classification, is the problem treated as a binary one by default?
> 2. How can I understand if the problem is handled as binary or multiclass?
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Re: Clarification on MultiClassClassifier

fpetrulio
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Re: Clarification on MultiClassClassifier

Eibe Frank-3
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