ListListA

ListListA is a parametric data structure designed to hold a collection of lists, where each inner list stores elements of the same type. It forms a two-level container in which the top-level structure indexes a sequence of buckets, and each bucket contains a contiguous sequence of elements. The design aims to balance dynamic resizing with locality and scalable iteration in scenarios where large or unevenly sized collections must be processed.

Internally, ListListA consists of a list of inner lists. The inner lists may be implemented as dynamic arrays or as linked lists, depending on the language and performance goals. A type parameter T ensures homogeneity of elements. Operations include appending new elements to the last bucket, inserting at a global index, removing by index, and accessing elements by their global position via a bucket selection plus offset.

Key operations include flattening, which concatenates all inner lists into a single sequence; map and reduce, which traverse all elements to produce results; and balance or reflow, which ensures buckets remain within a defined capacity by moving elements between buckets. Performance characteristics depend on the concrete implementation, but typical patterns include near-constant time for appending to a non-full bucket and linear time in the number of buckets for locating the target bucket, with constant-time access inside an array-based bucket.

Variants commonly exist, such as fixed-size buckets to improve locality or dynamic buckets that resize and rebalance as elements are added or removed. ListListA can be adapted to multi-dimensional data by nesting instances or by treating the top-level as a higher-level grid of buckets.

Applications include processing large block datasets, in-memory data structures with variable-length records, and cache-friendly iteration in streaming or parallel workloads.