def check_repeated(df,sel_col,id):
    """
    Checking for # of unique combinations of a selection of attributes.
    Different IDs sometimes do not guarantee uniqueness  
    
    Parameters:
    -----------
    df: pd.DataFrame
    sel_col: list of column names 
        Selection of columns where number of unique combinations is investigated
    id: Name of column with unique id
    Returns:
    --------
    dup_instances: int
        Number of instances with more than 1 appearance in the datasetbased on sel_col
    tot_instances: int
        # of instances in the population duplicated

    """
    df0 = df.groupby(by=sel_col).agg({id:"count"}).reset_index()

    dup_instances = (df0[id]>1).sum()
    tot_instances = df0[df0[id]>1][id].sum()

    return dup_instances,tot_instances