CountMap

Data structure for keeping a count of items.

npm install count-map

yarn add count-map

API

init

import CountMap from 'count-map';

const map = new CountMap({ array, hash, allowNegativeCounts });

| var | type | default | use | |-----|------|---------|-----| | array | Array | [] | Populate map right away with this array. | | hash | Function(key) => string | (key) => key.toString() | Hashing function. Used to group similar keys together, or to distinguish objects. | | allowNegativeCounts | boolean | false | Allow negative counts. Otherwise, the minimum is 0. |

Key management

• map.set(key, amount) – Sets ket count to amount. Creates entry if doesn't exist.
• map.delete(key) => boolean – Removes key from map if it exists. Returns false if key didn't exist.
• map.add(key, amount = 1) => count – Adds to key count. By default, increments by 1. Can provide amount to increment by that. Returns the new count for key.
• map.subtract(key, amount = 1) => count – Subtracts from key count. By default, decrements by 1. Can provide amount to decrement by that. Returns the new count for key.
• map.has(key) => boolean – Check if map has key.
• map.get(key) => count – Get count for key. If key doesn't exist, returns 0.
• map.concat(array, inPlace = false) => CountMap – Add contents of array to map. Operates on and returns clone unless inPlace is true.

Other

• map.keys() => Array – Returns array of unique keys. NOTE: If the hash sets two keys to be equal of each other, there will only be one instance of that saved as a representaive of the hash.
• map.entries() => Array[key, count] – Returns unique entries within the map.
• map.toArray() => Array – Creates an array, duplicating keys as many times as the count indicates. Leaves out keys with negative or empty counts.
• map.equals(otherMap) => boolean – Test if two CountMaps are equal. Specifically:
  • Are the hash functions the same?
  • Are the two negative modes equal?
  • Does each have the same keys and counts? NOTE: Keys may differ, but still return true depending on the hash function.
• map.clone() => CountMap – Duplicate CountMap.
• map.rehash() => this – Rehashes map. Use this if the hash function changes.