OSet

OSet is a term used in computer science to denote an ordered set, a data structure that combines the uniqueness guarantee of a set with the preservation of element order. An OSet stores each element at most once and yields elements in a defined sequence when iterated, typically reflecting the order in which elements were added. This makes it useful for deduplication tasks where the original ordering must be kept.

Core properties and operations commonly attributed to OSets include: add, remove, and membership tests, with iteration preserving insertion order. Depending on the implementation, there may also be standard set operations such as union, intersection, and difference, though the exact ordering behavior for these operations can vary. Some OSets optimize for fast membership checks and insertions, often using a hash table paired with a linked list or array to remember order. Others may prioritize different performance trade-offs, such as tree-based structures for ordered traversal by a key, though this is less typical when the primary goal is preserving insertion order.

Typical use cases include removing duplicates while maintaining input order, maintaining a sequence of unique identifiers, and preprocessing data where order matters but duplicates must be avoided. OSets are also used in scenarios like constructing lightweight caches, pipelines that require stable ordering, and any workflow where a unique collection must be enumerated in a predictable sequence.

Notes: the term OSet appears in multiple languages and libraries to denote an ordered set, but there is no universal standard. Users should consult the specific implementation’s documentation for exact semantics, performance characteristics, and ordering rules. See also: ordered set, LinkedHashSet, OrderedDict.