How to use the ngram.plot_top_ngrams function in ngram

def analyze_ngrams(transcripts, grouping_fn=ngram.group_text_by_category, output_dir=None, n=5):
    if output_dir is None:
        output_dir = stats_output

    if not os.path.exists(output_dir):
        os.makedirs(output_dir)

    top_ngrams_by_agent = []
    for agent_type in args.agent_types:
        grouped_utterances = grouping_fn(transcripts, agent_type)
        analyzer = ngram.NgramAnalyzer(grouped_utterances, n=n, agent_type=agent_type)

        top_ngrams_by_cat = analyzer.analyze()
        top_ngrams_by_agent.append(top_ngrams_by_cat)

    ngram.plot_top_ngrams(top_ngrams_by_agent, agents=args.agent_types,
                          output_dir=output_dir,
                          suffix="_{:d}grams".format(n))
    ngram.write_to_file(top_ngrams_by_agent, agents=args.agent_types,
                        output_dir=output_dir,
                        suffix="_{:d}grams".format(n))