def remove_background_noise(cov, min_cov):
    """ remove coverage background noise by set bins with cov < min_cov to 0
    :param cov: coverage data.frame
    :param min_cov: minimum coverage to include a window in analysis
    """
    cov_ft = cov.iloc[:, 4:].applymap(lambda x: 0 if x < min_cov else x)
    cov_ft.insert(0, 'chr', cov.chr)
    return cov_ft