Take in a dialogue (a sequence of tokenized utterances) and transform it into a
        sequence of sequences of one-hot vectors

def vectorize_dialogue_ohe(self, dia):
        """
        Take in a dialogue (a sequence of tokenized utterances) and transform it into a
        sequence of sequences of one-hot vectors
        """
        # we squeeze it because it's coming out with an extra empty
        # dimension at the front of the shape: (1 x dia x utt x word)
        return np.array([[self.vectorize_utterance_ohe(utt) for utt in dia]]).squeeze()