code: def plot_prep_methods(df, prep, prepi, out_file_base, outtype, title=None,
                        size=None):
      
      samples = df[(df["bamprep"] == prep)]["sample"].unique()
      assert len(samples) >= 1, samples
      out_file = "%s-%s.%s" % (out_file_base, samples[0], outtype)
      df = df[df["category"].isin(cat_labels)]
      _seaborn(df, prep, prepi, out_file, title, size)
      return out_file
docs: Plot comparison between BAM preparation methods.