# Array, list, map, set: pick by operation

Order, lookup, and uniqueness are different jobs.

ID: collections
Language: en
Revision: 2
Translation source revision: 2
Canonical: https://jujin.dev/en/guides/collections/

## Concept

Arrays hold indexed sequences; maps associate keys with values; sets hold unique entries. List implementations vary by language.

## Example

Array: draft → review → publish. Map: book-1 → 12000. Set: book-1 twice produces one entry.

## When to choose it

Arrays preserve sequence; maps expose keyed lookup; sets discard duplicate counts. JavaScript object keys use identity. Use stable IDs for identity. Keep multiple indexes only when their benefit justifies synchronization. [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Keyed_collections) · [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array)