Intro 🌐
Last time, we learned how to get data from our hash table .
Today, we'll learn how to get the keys of our Hash Table.
Requirements 💭
We need the following parts to get the keys from our Hash Table:
- a method to get the keys (
keys)
Starter Code ▶️
We start with the code with the set method, so that we can use the set method to add some data.
class Hashtable {
constructor() {
this.data = [];
this.size = 0;
}
hash(key) {
const chars = key.split("");
const charCodes = chars.map((char) => char.charCodeAt());
const charCodeSum = charCodes.reduce((acc, cur) => acc + cur);
return charCodeSum;
}
set(key, value) {
const hash = this.hash(key);
if (!this.data[hash]) {
this.data[hash] = [];
}
this.data[hash].push([key, value]);
this.size++;
}
}
If you are not familiar with the hash function, re-read this post.
Thoughts 💭
First, we should think about the constraints and possibilities:
- first, we declare an empty array for the keys
- then we iterate over the data array
- if there is data (= array of key-value pairs) at this specific index, iterate over this data (= the single key-value pairs)
- add the data (= key) to the keys array
- return the keys array
Example
We want to get the key-value pair with the key name.
// current hash table data:
[
[["age", 33]],
[
["name", "miku86"],
["mean", false],
],
];
// desired data:
["age", "name", "mean"];
Steps
// current hash table data:
[
[["age", 33]],
[
["name", "miku86"],
["mean", false],
],
];
// then we iterate over the data array
[["age", 33]];
// if there is data (= array of key-value pairs) at this specific index
// then iterate over this data (= the single key-value pairs)
["age", 33];
// add the data (= key) to the keys array
["age"];
// then we iterate over the data array
[
["name", "miku86"],
["mean", false],
];
// if there is data (= array of key-value pairs) at this specific index
// then iterate over this data (= the single key-value pairs)
["name", "miku86"];
// add the data (= key) to the keys array
["age", "name"];
// if there is data (= array of key-value pairs) at this specific index
// then iterate over this data (= the single key-value pairs)
["mean", false];
// add the data (= key) to the keys array
["age", "name", "mean"];
// desired data:
["age", "name", "mean"];
✅
Implementation ⛑
// a Hash Table class
class Hashtable {
constructor() {
this.data = [];
this.size = 0;
}
hash(key) {
const chars = key.split("");
const charCodes = chars.map((char) => char.charCodeAt());
const charCodeSum = charCodes.reduce((acc, cur) => acc + cur);
return charCodeSum;
}
set(key, value) {
const hash = this.hash(key);
if (!this.data[hash]) {
this.data[hash] = [];
}
this.data[hash].push([key, value]);
this.size++;
}
keys() {
// declare an empty array for the keys
const keys = [];
// iterate over the data array (I call a single array a "bucket")
for (let bucket of this.data) {
// if there is data (= array of key-value pairs) at this specific index
if (bucket) {
// iterate over this data (= the single key-value pairs)
for (let item of bucket) {
// add the data (= key) to the keys array
keys.push(item[0]);
}
}
}
// return the keys array
return keys;
}
}
Note: I'm using a for ... of-loop. If you don't know how this works, you can read about it on MDN. You can use whatever you want to use, a default for-loop, a for ... in-loop, a functional approach etc.
Result
// create a new hash table
const newHashtable = new Hashtable();
// add three new key-value pairs
newHashtable.set("name", "miku86");
newHashtable.set("mean", false);
newHashtable.set("age", 33);
// show the hash table data
console.log(newHashtable.data);
// [ <301 empty items>, [ [ 'age', 33 ] ], <115 empty items>, [ [ 'name', 'miku86' ], [ 'mean', false ] ] ]
// show the keys
console.log(newHashtable.keys());
// [ 'age', 'name', 'mean' ] ✅
✅
Next Part ➡️
We managed to write a function to get all keys, great work!
Next time, we'll learn how to get all values from our Hash Table.
Need some mentoring? Click here!
Further Reading 📖
Questions ❔
- How would you implement the
keys-function? - How would you write this code in a functional style?
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