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In computer science, an associative array, map, symbol table, or dictionary is an abstract data type composed of a collection of (key, value) pairs, such that each possible key appears at most once in the collection. Note that a dictionary is also known as a map.The dictionary problem is a classic computer science problem: the task of designing a data structure that maintains a set of data during 'search', 'delete', and 'insert' operations. There are many different types of implementations of dictionaries. Hash Table implementation Tree-Based Implementation (Self-balancing and Unbalanced trees) List based implementationWhen to use a DictionaryDictionaries are not a silver bullet ... Read More
Let's create a MyMap class so that it doesn't hide the actual Map class in JS. We'll create a container object that'll keep track of all our values that we add to the map. We'll also create a display function that prints the map for us. Exampleclass MyMap { constructor() { this.container = {}; } display() { console.log(this.container); } }In ES6, you can directly create a dictionary using the Map class. For example, Exampleconst map1 = new Map(); const map2 = new Map([ ["key1", "value1"], ["key2", "value2"] ]);Checking if ... Read More
Now we'll create the put method that'll allow us to put key-value pairs on the dictionary. Now using this we'll implement the put method.Note that JS has objects that act quite like dictionaries. We can just set the container's key property to value. Exampleput(key, value) { this.container[key] = value; }You can test this and the previous functions using − Exampleconst myMap = new MyMap() myMap.put("key1", "value1") myMap.put("key2", "value2") myMap.display() console.log(myMap.hasKey("key1")); console.log(myMap.hasKey("key3"));OutputThis will give the output −{key1: "value1", key2: "value2"} true falseIn ES6, you can put a key-value pair in a map using the set method. For example, Exampleconst myMap ... Read More
To remove an element from the dictionary, we first need to check if it exists in the dictionary.We'll use the hasKey method for that. Then we can directly delete it using the delete operator.We'll return a Boolean so that the place where we call this method can know whether the key already existed or not in the dictionary. Exampledelete(key) { if(this.hasKey(key)) { delete this.container[key]; return true; } return false; }You can test this using − Exampleconst myMap = new MyMap(); myMap.put("key1", "value1"); myMap.put("key2", "value2"); myMap.display(); myMap.delete("key2"); myMap.display();OutputThis will give the output ... Read More
We'll implement the get method that searches a given key in the dictionary. Exampleget(key) { if(this.hasKey(key)) { return this.container[key]; } return undefined; }Again, JS objects are very much implemented like dictionaries, hence have most of the functionality we can use directly without any more code needed. This is also heavily optimized, so you don't have to worry about the runtime of the function.You can test this using − Exampleconst myMap = new MyMap(); myMap.put("key1", "value1"); myMap.put("key2", "value2"); console.log(myMap.get("key1")) console.log(myMap.get("key2")) console.log(myMap.get("key3"))OutputThis will give the output −value1 value2 undefinedIn ES6, you have the same functionality using the ... Read More
Sometimes when working with a dictionary, we need only the keys of the dictionary as an array for some task. We can easily get the properties of an object using Object.keys. We'll use this method to return the keys from our container object. Examplekeys() { return Object.keys(this.container); }You can test this using − Exampleconst myMap = new MyMap(); myMap.put("key1", "value1"); myMap.put("key2", "value2"); console.log(myMap.keys());OutputThis will give the output −[ 'key1', 'key2' ]In ES6 Map, the same method is available that you can use. Note that it returns a MapIterator object, which you can convert to an array or use like a ... Read More
We'll implement a clear() function that simply clears the contents of the container. For example, Exampleclear() { this.container = {} }You can test this using − Exampleconst myMap = new MyMap(); myMap.put("key1", "value1"); myMap.put("key2", "value2"); myMap.display(); myMap.clear(); myMap.display();OutputThis will give the output −{ key1: 'value1', key2: 'value2' }You can use the clear method in the same way in ES6 maps as well. For example, Exampleconst myMap = new Map([ ["key1", "value1"], ["key2", "value2"] ]); console.log(myMap) myMap.clear(); console.log(myMap)OutputThis will give the output −Map { 'key1' => 'value1', 'key2' => 'value2' } Map {}Read More
Here we'll implement a for each function in our class and accept a callback that we can call on every key-value pair. Let's see how we can implement such a function − ExampleforEach(callback) { for (let prop in this.container) { // Call the callback as: callback(key, value) callback(prop, this.container[prop]); } }You can test this using − Exampleconst myMap = new MyMap(); myMap.put("key1", "value1"); myMap.put("key2", "value2"); myMap.forEach((k, v) => console.log(`Key is ${k} and value is ${v}`));OutputThis will give the output −Key is key1 and value is value1 Key is key2 and value is value2ES6 ... Read More
Here is the complete implementation of MyMap class − Exampleclass MyMap { constructor() { this.container = {}; } display() { console.log(this.container); } hasKey(key) { return key in this.container; } put(key, value) { this.container[key] = value; } delete(key) { if (this.hasKey(key)) { delete this.container[key]; return true; } return false; } get(key) { return this.hasKey(key) ? this.container[key] : undefined; ... Read More
Hash Table is a data structure which stores data in an associative manner. In a hash table, data is stored in an array format, where each data value has its own unique index value. Access to data becomes very fast if we know the index of the desired data.Thus, it becomes a data structure in which insertion and search operations are very fast irrespective of the size of the data. Hash Table uses an array as a storage medium and uses the hash technique to generate an index where an element is to be inserted or is to be located ... Read More