MapDictionary

A mapdictionary is a data structure that combines a mapping (map or dictionary) with nested dictionaries to form a two-level key-value store. The primary keys identify top-level categories or collections, while each value is itself a dictionary containing subkeys and their values. It is commonly implemented as a map of maps, such as Map<String, Map<K, V>> in statically typed languages or as an object of objects in dynamic languages.

Typical operations focus on compound keys. Setting and getting values use two-key access, for example by providing a top-level key and a subkey. Inner dictionaries can be manipulated independently, allowing additions, deletions, or updates within a given top-level category. In many implementations, lookups are performed in constant time on average, assuming underlying hash-based maps, with memory usage proportional to the number of top-level entries and inner entries.

Common use cases include hierarchical configuration data, localization where each language maps to a dictionary of strings, feature flag settings per category, and caching structures that partition data by category. The structure is especially convenient when the data naturally groups under a two-level namespace.

Relation to other structures: it resembles a JSON object with nested objects and maps directly to language-specific constructs such as Map<String, Map<String, V>> in Java or dict[str, dict[str, V]] in Python. Considerations include handling missing inner dictionaries, the complexity of deeper nesting, and potential thread-safety issues in concurrent environments. designers often choose mapdictionary for clear separation of top-level categories and their subentries.