Indexes an IMPUTE2 file.

    Args:
        fn (str): The name of the IMPUTE2 file.

def index_impute2(fn):
    """Indexes an IMPUTE2 file.

    Args:
        fn (str): The name of the IMPUTE2 file.

    """
    logger.info("Indexing {} (IMPUTE2)".format(fn))
    impute2_index(fn, cols=[0, 1, 2], names=["chrom", "name", "pos"], sep=" ")
    logger.info("Index generated")