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---
id: 587d8254367417b2b2512c6e
title: Perform a Difference on Two Sets of Data
challengeType: 1
---
## Description
< section id = 'description' >
In this exercise we are going to perform a difference on 2 sets of data. We will create a method on our < code > Set< / code > data structure called < code > difference< / code > . A difference of sets should compare two sets and return the items present in the first set that are absent in the second. This method should take another < code > Set< / code > as an argument and return the < code > difference< / code > of the two sets.
For example, if < code > setA = ['a','b','c']< / code > and < code > setB = ['a','b','d','e']< / code > , then the difference of setA and setB is: < code > setA.difference(setB) = ['c']< / code > .
< / section >
## Instructions
< section id = 'instructions' >
< / section >
## Tests
< section id = 'tests' >
```yml
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tests:
- text: Your < code > Set</ code > class should have a < code > difference</ code > method.
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testString: 'assert(function(){var test = new Set(); return (typeof test.difference === "function")}, "Your < code > Set< / code > class should have a < code > difference< / code > method.");'
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- text: The proper collection was returned
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testString: 'assert(function(){var setA = new Set(); var setB = new Set(); setA.add("a"); setA.add("b"); setA.add("c"); setB.add("c"); setB.add("d"); var differenceSetAB = setA.difference(setB); return (differenceSetAB.size() === 2) & & (differenceSetAB.values() === [ "a", "b" ])}, "The proper collection was returned");'
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```
< / section >
## Challenge Seed
< section id = 'challengeSeed' >
< div id = 'js-seed' >
```js
function Set() {
// the var collection will hold the set
var collection = [];
// this method will check for the presence of an element and return true or false
this.has = function(element) {
return (collection.indexOf(element) !== -1);
};
// this method will return all the values in the set
this.values = function() {
return collection;
};
// this method will add an element to the set
this.add = function(element) {
if(!this.has(element)){
collection.push(element);
return true;
}
return false;
};
// this method will remove an element from a set
this.remove = function(element) {
if(this.has(element)){
var index = collection.indexOf(element);
collection.splice(index,1);
return true;
}
return false;
};
// this method will return the size of the collection
this.size = function() {
return collection.length;
};
// this method will return the union of two sets
this.union = function(otherSet) {
var unionSet = new Set();
var firstSet = this.values();
var secondSet = otherSet.values();
firstSet.forEach(function(e){
unionSet.add(e);
});
secondSet.forEach(function(e){
unionSet.add(e);
});
return unionSet;
};
// this method will return the intersection of two sets as a new set
this.intersection = function(otherSet) {
var intersectionSet = new Set();
var firstSet = this.values();
firstSet.forEach(function(e){
if(otherSet.has(e)){
intersectionSet.add(e);
}
});
return intersectionSet;
};
// change code below this line
// change code above this line
}
```
< / div >
< / section >
## Solution
< section id = 'solution' >
```js
function Set() {var collection = []; this.has = function(e){return(collection.indexOf(e) !== -1);};this.values = function() {return collection;};this.add = function(element) {if (!this.has(element)) {collection.push(element);return true;} else {return false;}};this.remove = function(element) {if(this.has(element)) {var i = collection.indexOf(element);collection.splice(i, 1);return true;}return false;};this.size = function() {return collection.length;};this.union = function(set) {var u = new Set();var c = this.values();var s = set.values();c.forEach(function(element){u.add(element);});s.forEach(function(element){u.add(element);});return u;};this.intersection = function(set) {var i = new Set();var c = this.values();c.forEach(function(element){if(s.has(element)) i.add(element);});};this.difference = function(set) {var d = new Set();var c = this.values();c.forEach(function(e){if(!set.has(e)) d.add(e);});};}
```
< / section >