How to build a hash table in JavaScript?
Hash tables are a powerful and versatile data structure used extensively in programming. They are essentially an object that generates a hash to efficiently store and search data. In this guide, we will explore how to build a hash table in JavaScript, highlighting key steps and essential concepts.
Where do we start?
The first step in creating a hash table is to define the class in JavaScript. Within this class, we must include a constructor that initializes the size of the hash table. This translates into the number of "buckets" or compartments that will be available to store data. Here is an example of what this looks like in code:
{class HashTable { constructor(size) { this.data = new Array(size); }}
In this case, the array created has 50 spaces, allowing you to store data efficiently.
How is a hash function implemented?
The hash function is a critical piece in generating a unique identifier for each piece of data we want to store. Although, in a real project, a hash function is rarely implemented from scratch, for learning purposes, you can build a simple one that generates a random number related to the key entered:
hashFunc(key) { let hash = 0; for (let i = 0; i < key.length; i++) { hash = (hash + key.charCodeAt(i) * i) % this.data.length; } return hash;}
It is important to remember that, in most applications, already existing hash functions that are robust and optimized are used.
How to add elements in the hash table?
The set method is key to adding elements to the hash table. This function takes two important parameters: the key and the value. It uses the key to generate a hash that will indicate the location of the value within the hash table:
set(key, value) { const address = this.hashFunc(key); if (!this.data[address]) { this.data[address] = []; } this.data[address].push([key, value]); return this.data;}
This method handles collisions efficiently. If two different keys generate the same hash, the value is placed in a sublist of the corresponding bucket, preserving both entries.
What happens during a collision?
A collision occurs when two different keys generate the same hash. In this scenario, it is crucial to handle the collision to avoid data loss. By implementing the use of chained lists (sublists within a bucket), we ensure that each entry is properly preserved:
set(key, value) { const address = this.hashFunc(key); if (!this.data[address]) { this.data[address] = []; } this.data[address].push([key, value]);}
In this way, each bucket can contain multiple key-value pairs, ensuring that information is not overwritten.
How does it behave when interacting with the JavaScript terminal?
In the development environment, we can test the performance of our hash table. We start by testing if the buckets are created correctly:
const myHashTable = new HashTable(50);
Subsequently, we store exemplary data:
myHashTable.set('Diego', 1990);myHashTable.set('Mariana', 1998);myHashTable.set('Alejandra', 2000);
We verify the integrity of our system by observing that each data is stored without being overwritten. In the face of collisions, we see that the chained list mechanism works perfectly.
Now, you have a solid understanding of how to build a hash table in JavaScript. As you progress, you will see how concepts such as storage efficiency and collision handling are applicable in multiple contexts in software development. Keep learning and experimenting!
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