---
title: Core · Collections
description: Data structures and iteration.
canonical: https://rubydoc.ai/docs/core-collections.md
source: RubyDoc.AI
---

# Core · Collections

Data structures and iteration.

- [Array](https://docs.ruby-lang.org/en/master/Array.html) — Ordered, mutable list.
- [Hash](https://docs.ruby-lang.org/en/master/Hash.html) — Key/value dictionary preserving insertion order.
- [Set](https://docs.ruby-lang.org/en/master/Set.html) — Unordered collection of unique values.
- [Enumerable](https://docs.ruby-lang.org/en/master/Enumerable.html) — Mixin providing map, select, reduce & friends.
- [Enumerator](https://docs.ruby-lang.org/en/master/Enumerator.html) — Externalize iteration; build lazy pipelines.
- [Comparable](https://docs.ruby-lang.org/en/master/Comparable.html) — Mixin for ordering via <=>.

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Part of the [RubyDoc.AI](https://rubydoc.ai) documentation index. See also [docs.md](https://rubydoc.ai/docs.md) and [llms.txt](https://rubydoc.ai/llms.txt).