CODEWITHSUNDEEP
classificationvowpalwabbit
Vivek Aditya
Vivek Aditya

Reputation: 1173

Error Correcting Tournaments (ect) Multi Class Classification in Vowpal Wabbit

I tried to go through this paper which describes the ECT algorithm but could not make much out of it.

I know it is different from one-against-al (oaa) and even performs better than oaa.I wanted a simple explanation about how ect works.

Upvotes: 2

Views: 476

Answers (1)

Martin Popel
Martin Popel

Reputation: 2670

ECT and Filter trees are useful (only) if you have a very big number of output labels (classes), let's say N=1000. With OAA (one-against-all), it would mean to do N binary classification tasks for each example (during both training and testing). With ECT you can make the prediction much faster: log(N). You can imagine Filter trees (which are the basis of ECT) as a decision tree where in each node you ask whether the example belongs to one set of labels or another set of labels (using all the features, unlike original decision trees).

In general, ECT is worse (in terms of loss or accuracy) than OAA (but in some cases it may be almost as good as OAA). With N=10 labels, you should try OAA first. With N>1000, OAA is too slow (and even the accuracy is low), you should try ECT (or --log_multi or --csoaa_ldf in VW, if you can preselect a smaller number of labels which are relevant for each example).

See http://cilvr.cs.nyu.edu/diglib/lsml/logarithmic.pdf

Upvotes: 3

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