def __get_all_common_columns(data_dict):
    """
    Computes an array of (unique) common columns to the data frames in data_dict
    :param data_dict: Dictionary of data frames
    :return: array.
    """
    common_columns = []
    for i, k in enumerate(data_dict.keys()):
        if i == 0:
            common_columns = data_dict[k].columns
        else:
            common_columns = common_columns.intersection(data_dict[k].columns)
    if len(common_columns.values) == 0:
        raise ValueError(
            'Data frames should have homogeneous columns with the same name to use for computing intersections'
            )
    return common_columns.unique()
