def get_missing_ids(raw, results):
    """
    Compare cached results with overall expected IDs, return missing ones.
    Returns a set.
    """
    all_ids = set(raw.keys())
    cached_ids = set(results.keys())
    print("There are {0} IDs in the dataset, we already have {1}. {2} are missing.".format(len(all_ids), len(cached_ids), len(all_ids) - len(cached_ids)))
    return all_ids - cached_ids