Create an 'other' category for classregtree?

I'm using classregtree to create a decision tree for analyzing low resolution images and determining their taxanomic classification. I have created three categories of interest. When predicting data, if the data is not one of the three categories, I would like it to go in an 'other' category and/or not be fit into one of my existing categories. Is there a way to do this other than creating another category that consists of random and greatly varying taxa?

Answer 1

[Ilya]

It is not entirely clear from your post if you are talking about a categorical predictor (one of the variables in X) or the categorical response (Y, or class labels). I will assume the latter.

classregtree can only predict into one of the classes included in the training data. How would you determine if an observation is not one of the three categories? If you can do it, classregtree can do it too, as long as you have enough data for this 4th category and use these data to grow the tree.