Dicts

Dicts, short for dictionaries, are data structures that store pairs of keys and values. They provide fast lookup, insertion, and deletion by key and are used to model associative arrays, records, configurations, and data that resembles JSON.

Most dicts are implemented as hash tables. Keys must be hashable, and values can be of any type. Average-case complexity for lookups, insertions, and deletions is O(1). Implementations resize to maintain performance as the number of entries grows; resizing may temporarily affect performance.

Collisions—situations where different keys hash to the same location—are handled by techniques such as chaining or open addressing. Some languages provide ordered or sorted variants, affecting iteration order and performance. For example, Python's dict preserves insertion order since Python 3.7.

Common uses include counting occurrences, storing configuration settings, representing records with named fields, and providing fast access to data retrieved from other structures or networks. Dicts map naturally to JSON objects and interchange formats; many languages offer direct equivalents or interoperable representations.

Variants and language support: In Python, dict is a built-in mutable mapping type. In Java, the Map interface has implementations such as HashMap (un-ordered), LinkedHashMap (insertion-ordered), and TreeMap (sorted). In JavaScript, Map provides explicit key-value mapping, while plain objects serve a similar role for string keys. Data interchange formats like JSON map to dict-like structures in many languages.