Chris Parry Chris Parry - 1 month ago 9
Python Question

Adapting binary stacking example to multiclass

I have been studying this example of stacking. In this case, each set of K-folds produces one column of data, and this is repeated for each classifier. I.e: the matrices for blending are:

dataset_blend_train = np.zeros((X.shape[0], len(clfs)))
dataset_blend_test = np.zeros((X_submission.shape[0], len(clfs)))


I need to stack predictions from a multiclass problem (probs 15 different classes per sample). This will produce an n*15 matrix for each clf.

Should these matrices just be concatenated horizontally? Or should they be combined in some other way, before logistic regression is applied? Thanks.

Answer

You can adapt the code to the multi-class problem in two ways:

  1. Concatenate horizontally the probabilities, that is you will need to create: dataset_blend_train = np.zeros((X.shape[0], len(clfs)*numOfClasses)) dataset_blend_test = np.zeros((X_submission.shape[0], len(clfs)*numOfClasses))
  2. Instead of using probabilities, use the class prediction for the base models. That way you keep the arrays the same size, but instead of predict_proba you just use predict.

I have used both successfully, but which works better may depend on the dataset.

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