Implement a Multimap in JavaScript

This post will discuss the possible ways to implement a multimap in JavaScript.

A multimap is a data structure that maps a key to a collection of values, such as an array or a set. A multimap can be useful for storing and retrieving multiple values associated with the same key, such as phone numbers, email addresses, or locations. There is no built-in multimap class in JavaScript, but we can implement one using various methods. Here are some possible ways to implement a multimap in JavaScript:

1. Using an object with arrays as values

A simple and convenient way to implement a multimap is to use an object with arrays as values. This allows easy access and modification of the values using the object properties or functions like Object.keys(), Object.values(), Object.entries(), etc. However, this may not be the most efficient or elegant way to implement a multimap, as it requires checking if a property exists before adding or deleting values, and it does not have built-in functions for common operations like getting all values or deleting all keys. We have to use the array functions and properties to work with the values for a given key. For example, we can create a multimap that maps string to numbers like this:

let multimap = {};

multimap["Joseph"] = [1, 2];

multimap["Olivia"] = [3];

multimap["Samuel"] = [4, 5, 6];

// add a new value for a key

multimap["Joseph"].push(7);

// remove a value for a key

let index = multimap["Samuel"].indexOf(5);

if (index > -1) {

multimap["Samuel"].splice(index, 1);

}

// iterate over the keys and values of the multimap

for (let key in multimap) {

console.log(key, multimap[key]);

}

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Output:

Joseph [1, 2, 7]
Olivia [3]
Samuel [4, 6]

2. Using a `Map` object with arrays as values

Another way is to use a Map object as the underlying data structure, and store the values as arrays or sets for each key. A Map object is a collection of key-value pairs that preserves the insertion order and allows any type of value as a key. We can use the Map functions and properties to access and modify the values for a given key. For example, we can create a multimap that maps words to synonyms like this:

let multimap = new Map();

multimap.set("big", ["large", "huge", "enormous"]);

multimap.set("small", ["tiny", "little", "miniature"]);

// add a new value for a key

multimap.get("big").push("gigantic");

// remove a value for a key

let synonyms = multimap.get("small");

let index = synonyms.indexOf("tiny");

if (index > -1) {

synonyms.splice(index, 1);

}

// iterate over the keys and values of the multimap

for (let [key, value] of multimap) {

console.log(key, value);

}

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Output:

big [‘large’, ‘huge’, ‘enormous’, ‘gigantic’]
small [‘little’, ‘miniature’]

This function is more robust and flexible than using a plain object, but it requires more code and memory to create and maintain the Map object.

3. Using Collections.js library

A third way is to use an external library or package, such as Collections.js, which provides various data structures and algorithms for JavaScript. We can use the MultiMap class from this library, which inherits from the Map class and adds functions and properties to handle multiple values for each key. We can add or remove values for a key using the add or delete functions, which are overridden from the Map class. We can also use other functions and properties from the Map class or the MultiMap class, such as get, set, has, keys, values, entries, forEach, map, filter, reduce, etc. Here’s an example of how we can use the MultiMap class:

// Include the Collections.js library

let MultiMap = require("collections/multi-map");

// Create an instance of the MultiMap class

let multimap = new MultiMap();

// Add some key-value pairs to the multimap

multimap.add("red", "apple");

multimap.add("red", "cherry");

multimap.add("yellow", "banana");

multimap.add("green", "lime");

multimap.add("green", "pear");

console.log(multimap.get("red")); // ["apple", "cherry"]

console.log(multimap.has("blue")); // false

console.log(multimap.keys()); // ["red", "yellow", "green"]

console.log(multimap.values()); // [["apple", "cherry"], ["banana"], ["lime", "pear"]]

// [["red", ["apple", "cherry"]], ["yellow", ["banana"]], ["green", ["lime", "pear"]]]

console.log(multimap.entries());

// Delete a key-value pair

multiMap.delete("green", "lime");

console.log(multimap.get("green")); // ["pear"]

// Iterate over the keys, values, or entries of the multimap

multimap.forEach((value, key) => console.log(key, value));

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This function is convenient and powerful, but it requires installing and importing the external library or package, which may not be available or compatible with our environment or project.

That’s all about the possible ways to implement a multimap in JavaScript.

Implement a Multimap in JavaScript

1. Using an object with arrays as values

2. Using a Map object with arrays as values

3. Using Collections.js library

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2. Using a `Map` object with arrays as values