def _format_num_reads(reads):
    """Format number of reads as k, M, or G"""
    fmt_reads = []
    for x in reads:
        if int(x) < 1e6:
            fmt_reads.append("{:.1f}k".format(int(x)/1e3))
        elif int(x) > 1e9:
            fmt_reads.append("{:.1f}G".format(int(x)/1e9))
        else:
            fmt_reads.append("{:.1f}M".format(int(x)/1e6))
    return fmt_reads