Set data structure of Java in javascript/jQuery

Question

Is there any way to create Set data structure(Unique Collections) like java in javascript?

Answer 1

For a set of strings, I would just use a object with the value true.

var obj = {};
obj["foo"] = true;
obj["bar"] = true;
if(obj["foo"])
{
 // foo in set
}

This is basically how HashSet works in Java, assuming the JavaScript object is implemented as a hashtable (which is typical).

• Eran Medan: So how to remove an object from that set? obj["foo"]=null? or obj["foo"]=false?
• Matthew Flaschen: @Eran, delete obj["foo"] or delete obj.foo.
• Eran Medan: Thanks for teaching an old dog a new trick :) this is amazing I never encountered it in JS, brings me back to my C++ days though...
• Matthew Flaschen: @Eran, yeah. As you probably know, it's quite different in JavaScript, given that it's garbage-collected and there are no destructors.

Answer 2

I have written a JavaScript implementation of a hash set that is similar to Java's HashSet. It allows any object (not just strings) to be used as a set member. It's based on the keys of a hash table.

http://code.google.com/p/jshashtable/downloads/list

Documentation will follow shortly, I promise. For now, the source should give you the API pretty clearly, and here's an example:

var s = new HashSet();
var o1 = {name: "One"}, o2 = {name: "Two"};
s.add(o1);
s.add(o2);
s.add(o2);
s.values(); // Array containing o1 and a single reference to o2

Answer 3

Well though it seemed to be a common problem, and I found what seemed to be a good Set class on the net that supports objects, I wanted a simpler one and ended up writing one myself... in case anyone else finds it useful...

/**
 * A Javascript Class that represents a set of unique values
 * 
 * Usage:
 * 
 * var s = new jsSet();
 * 
 * s.add('a1'); s.add('a2');
 * 
 * s.list(); >> ['a1','a2']
 * 
 * s.remove('a1'); s.list(); >> ['a2']
 * 
 * s.contains('a1') >> false
 * 
 * s.contains('a2') >> true
 * 
 * can be chained
 * s.add(null).add('hello');
 * 
 * add array
 * s.addAll([ null, 'a', 'b' ]);
 * 
 * remove array
 * s.addAll([ null, 'a', 'b' ]);
 * 
 * retrieve the elements as a list
 * s.list();
 * 
 * size of the set
 * s.size();
 * 
 */
function jsSet() {
 // null can also be an element of the set, but needs
 // a separate indication to differentiate it from
 // the string "null" as well
 this.isNullAdded = false;
 // private member variable hence no 'this'
 var map = {};
 // Scope for optimization
 // could be cached instead of generating each time
 // this.uniqueList = [];
 // returns true if the element is in this set, false otherwise
 this.contains = function(key) {
 if (key === null)
 return this.isNullAdded;
 else if (key === undefined)
 return false;
 else
 return map[key] ? true : false;
 };
 // adds the element to the set
 this.add = function(val) {
 if (val === null)
 this.isNullAdded = true;
 else if (val !== undefined)
 map[val] = true;
 return this;
 };
 // adds all the elements of the array to the set
 this.addAll = function(val) {
 if (val !== null && val !== undefined && val instanceof Array) {
 for ( var idx = 0; idx < val.length; idx++) {
 this.add(val[idx]);
 }
 }
 return this;
 };
 // removes the specified element from the set
 this.remove = function(val) {
 if (val === null)
 this.isNullAdded = false;
 else if (val !== undefined)
 delete map[val];
 return this;
 };
 // removes all the element in the array from the set
 this.removeAll = function(val) {
 if (val !== null && val !== undefined && val instanceof Array) {
 for ( var idx = 0; idx < val.length; idx++) {
 console.log('val: %s:%s', idx, val[idx]);
 this.remove(val[idx]);
 }
 }
 return this;
 };
 // empties the set of all values
 this.clear = function() {
 this.isNullAdded = false;
 map = {};
 return this;
 };
 // returns the number of elements in the set
 this.size = function() {
 return this.list().length;
 };
 // returns true if the set is empty, false otherwise
 this.isEmpty = function() {
 return this.list().length > 0? false: true;
 };
 // returns the elements of the set as a list
 this.list = function() {
 var arr = [];
 if (this.isNullAdded)
 arr.push(null);
 for (o in map) {
 // protect from inherited properties such as
 // Object.prototype.test = 'inherited property';
 if (map.hasOwnProperty(o))
 arr.push(o);
 }
 return arr;
 };
};

• msanjay: if we don't need null values in the Set, then we can just do a remove(null) after adding all elements.

Answer 4

In modern browsers, I would use a Map using only the keys' methods. For example:

• New set: let mySet = new Map();
• Add element: mySet.set(element, 1)
• Remove element: mySet.delete(element)
• Contains element: mySet.has(element)

You can make your own wrapper if you don't want to see the Map implementation. This approach is how Java HashSet is implemented, it uses a HashMap and only uses the key methods.

Answer 5

Javascript now provides (part of es6) Set Api, which can be used to create unique collection.

var set = new Set([1,1,2,3]);
set.add(1);
set.add(4); 

For more info, visit - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set