It’s because accuracy_score is for classification tasks only. For regression you should use something different, for example: Where X_test is samples, y_test is corresponding ground truth values. It will compute predictions inside.
I had the same problem. You can try to use small trick to equalize classes of training and test set. Bind the first row of training set to the test set and than delete it. For your example it should look like this:
No, there isn’t. Somebody’s working on this and the patch might be merged into mainline some day, but right now there’s no support for categorical variables in scikit-learn except dummy (one-hot) encoding.