# martinus/unordered_dense

A fast & densely stored hashmap and hashset based on robin-hood backward shift deletion

Repository: https://github.com/martinus/unordered_dense
Canonical: https://ross.abutalabs.com/products/unordered_dense
Language: C++
License: MIT
License Family: permissive
Topics: c-plus-plus, cpp17, cpp, hash, hash-tables, header-only-library, no-dependencies, stl-containers, unordered-map, unordered-set
Last push: 2026-08-23T11:14:39+00:00

## Health v2 (maintenance only)
Score: 99/100 (v2, computed 2026-09-02T17:46:02.011165+00:00)
- activity 99, release rhythm 98, longevity 100
- inputs: {"age_days": 1531, "days_push": 10, "days_rel": 17, "gap_med": 6, "n_releases_24m": 8}
- flags: none
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 1457, forks 116 (observed 2026-08-28T04:04:47.062641+00:00)

## What it is
A fast, densely stored C++17 hashmap and hashset library based on robin-hood hashing with backward shift deletion. It provides drop-in replacements for std::unordered_map and std::unordered_set that are typically much faster, plus segmented variants with lower peak memory usage.

## Use cases
- replace std::unordered_map with a faster hashmap
- speed up hash set lookups in C++ code
- store hash maps densely to reduce memory usage
- get stable references on insert with segmented_map
- use a header-only hash table with no dependencies

## When to choose
- you need faster unordered containers than the STL and can tolerate weaker iterator stability
- you want a header-only, dependency-free C++17 container library
- memory locality and iteration speed matter more than pointer stability

## When to avoid
- you require full iterator and reference stability across rehashing and deletion
- you need exact std::unordered_map API compatibility in every detail

## Facets
- artifact type: library
- maturity: stable
- function: caching, developer-tools
- domain: performance, developer-tools
- platform: cpp, cross-platform
- tags: hashmap, hashset, robin-hood, header-only, stl-containers, cpp17, data-structures, algorithms

## Member repositories
- martinus/unordered_dense (main) score 99

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:04:47.062641+00:00.
- Health v2: computed from the inputs above; adoption is never an input.
- Inferred fields (summary, facets, guidance): AI-extracted, prompt v1, taxonomy v1, on 2026-08-30T04:35:33.701543+00:00, confidence not recorded.
  - readme: https://github.com/martinus/unordered_dense (fetched 2026-08-28T04:04:47.062641+00:00, sha b777275adcca)
- Data as of 2026-08-30T08:39:29.467469+00:00.