OrderedMap

An OrderedMap is a data structure that combines the features of a traditional map or dictionary with the ability to maintain the order of element insertion. Unlike standard hash maps, which do not guarantee any specific order of their entries, OrderedMaps preserve the sequence in which key-value pairs are added. This capability is particularly useful when the order of data matters, such as in configuration files, serialization, or user interface applications.

Typically implemented using a combination of a hash table and a linked list, an OrderedMap allows for efficient key-based lookup, insertion, and deletion, while also maintaining a predictable iteration order. When a new entry is added, it is appended to the end of the internal sequence; removing or rearranging entries updates both the hash table and the order sequence accordingly.

Many programming languages provide native or library-based implementations of OrderedMap. For example, Python's collections.OrderedDict (prior to Python 3.7) explicitly maintains insertion order, while in Java, the LinkedHashMap class offers similar functionality. In JavaScript, the Map object inherently preserves insertion order.

OrderedMaps are advantageous in scenarios requiring deterministic iteration order alongside fast lookups. However, they may incur additional memory overhead compared to standard hash maps due to the linked list management. Overall, the choice of using an OrderedMap depends on the specific requirements of data ordering and access efficiency in a given application.