This one time transformer removes specified columns in the input dataset
Split the dataset and store the splits with the specified keys into DKV It determines the frame which is passed on the output in the following order: 1) If the train key is specified using setTrainKey method and the key is also specified in the list of keys, then frame with this key is passed on the output 2) Otherwise, if the default key - "train.hex" is specified in the list of keys, then frame with this key is passed on the output 3) Otherwise the first frame specified in the list of keys is passed on the output