def variance_id(csv_name):
    """
    Extract an integer slope parameter from the filename.
    :param csv_name: The name of a csv file of the form NWS-<SLP>-0.5.csv
    :return: int(<SLP>)
    """
    filename = csv_name.split("-")[2]
    return float(".".join([x for x in filename.split(".") if x != "csv"]))