Subsets And SuperSets

Part of the Logic & Flow section of Coddy's JavaScript journey — lesson 40 of 65.

A set A is a subset of set B if every element of A is also an element of B. Conversely, B is a superset of A if it contains all elements of A.

Two sets are equal if they contain exactly the same elements. For example let's create some tests:

const setA = new Set([1, 2, 3]);
const setB = new Set([1, 2, 3, 4, 5]);
const setC = new Set([1, 2, 3]);
const setD = new Set([6, 7, 8]);

Function to check if setA is a subset of setB:

function isSubset(setA, setB) {
  return [...setA].every(element => setB.has(element));
}

Function to check if setA is a superset of setB:

function isSuperset(setA, setB) {
  return isSubset(setB, setA);
}

Function to check if two sets are equal:

function areEqual(setA, setB) {
  return setA.size === setB.size && isSubset(setA, setB);
}

Testing subset relationship:

// A is subset of B? 
isSubset(setA, setB) // true
// B is subset of A? 
isSubset(setB, setA) // false
// D is subset of B? 
isSubset(setD, setB) // false

Testing superset relationship:

// B is superset of A?
isSuperset(setB, setA) // true
// A is superset of B?
isSuperset(setA, setB) // false

Testing equality:

// A equals C?
areEqual(setA, setC) // true
// A equals B?
areEqual(setA, setB) // false
// A equals D?
areEqual(setA, setD) // false

Challenge

Easy

Create a function called analyzeSetRelations that takes two arrays as parameters: arr1 and arr2. The function should convert the arrays to sets and return an object with the following properties:

isSubset: a boolean indicating whether set1 is a subset of set2
isSuperset: a boolean indicating whether set1 is a superset of set2
isEqual: a boolean indicating whether set1 and set2 have exactly the same elements

Cheat sheet

A set A is a subset of set B if every element of A is also an element of B. Conversely, B is a superset of A if it contains all elements of A. Two sets are equal if they contain exactly the same elements.

Check if setA is a subset of setB:

function isSubset(setA, setB) {
  return [...setA].every(element => setB.has(element));
}

Check if setA is a superset of setB:

function isSuperset(setA, setB) {
  return isSubset(setB, setA);
}

Check if two sets are equal:

function areEqual(setA, setB) {
  return setA.size === setB.size && isSubset(setA, setB);
}

Try it yourself

function analyzeSetRelations(arr1, arr2) {
    let set1 = new Set(arr1);
    let set2 = new Set(arr2);

    // Use .every() and .has() to check set relations
    let isSubset = false;   // TODO: check if every element of set1 exists in set2
    let isSuperset = false; // TODO: check if every element of set2 exists in set1
    let isEqual = false;    // TODO: check if both sets have the same size and isSubset is true

    return {
        isSubset: isSubset,
        isSuperset: isSuperset,
        isEqual: isEqual
    };
}