2016-09-26 08:16:51 -0500 asked a question Exception on training RTrees with categorical data and categorical responses Hi all, I get the following exception when trying to train an RTree with categorical data and more than two different categorical responses: OpenCV Error: Assertion failed (sum > 0) in findSplitCatClass, file /home/.../dev/opencv-3.1.0/modules/ml/src/tree.cpp, line 880 terminate called after throwing an instance of 'cv::Exception' what(): /home/.../dev/opencv-3.1.0/modules/ml/src/tree.cpp:880: error: (-215) sum > 0 in function findSplitCatClass My sample code is as follows: vector responses; responses.push_back(2); responses.push_back(0); responses.push_back(0); responses.push_back(0); responses.push_back(0); responses.push_back(1); Mat resp; Mat(responses).copyTo(resp); Mat dat; vector data(6, 0); Mat(data).copyTo(dat); Mat types(2, 1, CV_8U); types.at(0) = VAR_CATEGORICAL; types.at(1) = VAR_CATEGORICAL; Ptr tdata = TrainData::create(dat, ROW_SAMPLE, resp, noArray(), noArray(), noArray(), types); Ptr model; model = RTrees::create(); model->setMinSampleCount(4); int success = model->train(tdata);  The exception does not occur if only two different response values are present (e.g. change the 1 to 2 or the 2 to 1) or if the data or the responses are chosen as type VAR_ORDERED. What is the reason for the exception and how can I avoid it?