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

def facet_freq_plot(freq_csv, caller):
    """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
    """
    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)