code: def facet_freq_plot(freq_csv, caller):
      
      out_file = "%s.png" % os.path.splitext(freq_csv)[0]
      plt.ioff()
      sns.set(style='dark')
      df = pd.read_csv(freq_csv)
      g = sns.FacetGrid(df, row="vtype", col="valclass", margin_titles=True,
                        col_order=["TP", "FN", "FP"], row_order=["snp", "indel"],
                        sharey=False)
      g.map(plt.hist, "freq", bins=20, align="left")
      g.set(xlim=(0.0, 1.0))
      g.fig.set_size_inches(8, 6)
      g.fig.text(.05, .97, caller, horizontalalignment='center', size=14)
      g.fig.savefig(out_file)
docs: Prepare a facet plot of frequencies stratified by variant type and status (TP, FP, FN).
  
      Makes a nice plot with the output from validate.freq_summary