def _extract_keys_to_unique_list(lists_of_dictionaries):
    """
    Extract the keys for a list of dictionaries and merge them into a unique list.

    :param lists_of_dictionaries: List of dictionaries to pull unique keys from.
    :type lists_of_dictionaries:  list(dict)
    :return: Merged list of keys into a unique list.
    :rtype:  list
    """
    merged_list = list(lists_of_dictionaries[0].keys())
    for idx, d in enumerate(lists_of_dictionaries):
        if idx != 0:
            merged_list = merged_list + list(set(list(d.keys())) - set(merged_list))
    return merged_list