coherence               Helper function for calculating coherence for a
                        single topic's worth of terms
contain_equal_docs      Helper function to check that a topic model and
                        a dtm contain the same number of documents
dist_from_corpus        Calculate the distance of each topic from the
                        overall corpus token distribution
doc_prominence          Calculate the document prominence of each topic
                        in a topic model
mean_token_length       Calculate the average token length for each
                        topic in a topic model
n_topics                Helper function to determine the number of
                        topics in a topic model
tf_df_dist              Calculate the distance between token and
                        document frequencies
tf_df_dist_diff         Helper function to calculate the Hellinger
                        distance between the token frequencies and
                        document frequencies for a specific topic's top
                        N tokens
topic_coherence         Calculate the topic coherence for each topic in
                        a topic model
topic_diagnostics       Calculate diagnostics for each topic in a topic
                        model
topic_exclusivity       Calculate the exclusivity of each topic in a
                        topic model
topic_size              Calculate the size of each topic in a topic
                        model
