How to Create an Array using Intersection of two Arrays in JavaScript ? (original) (raw)

Last Updated : 21 May, 2024

In this article, we will try to understand how to create an array using the intersection values of two arrays in JavaScript using some coding examples.

**For Example:

arr1 = [1, 3, 5, 7, 9, 10, 14, 15]
arr2 = [1, 2, 3, 7, 10, 11, 13, 14]

result_arr = [1, 3, 7, 10, 14]

**Approach 1:

• We will see the native approach to solving our problem statement which is how to create an array using the two arrays' intersection values.
• This approach uses two simple for-loops which will run on both the arrays so created earlier and an if-statement which checks the values of both arrays.
• After checking the values from both arrays, we will actually push the values into the new array and return the array from the function, and later display the result over the browser's console.

**Example:

JavaScript `

let first_array = [1, 3, 5, 7, 9]; let second_array = [2, 3, 4, 5, 6, 9];

let res_arr = (first_array, second_array) => { let new_array = []; for (let i = 0; i < first_array.length; i++) { for (let j = 0; j < second_array.length; j++) { if (first_array[i] === second_array[j]) { new_array.push(first_array[i]); } } } return new_array; };

console.log("Array obtained is :"); console.log(res_arr(first_array, second_array));

`

**Output:

Array obtained is :
[ 3, 5, 9 ]

**Approach 2:

• In this approach, we will try to visualize a better approach as compared to what we have witnessed in the previous example and we will try to avoid the extra overhead so required previously.
• In this example, we will use the filter() method as well as the includes() method of Arrays in JavaScript which will eventually filter elements based on their inclusion in both the arrays themselves.
• Later after filtering the elements from both arrays, we will display the array as output in the console.

**Example:

JavaScript `

let first_array = [1, 3, 5, 7, 9]; let second_array = [2, 3, 4, 5, 6, 9];

let new_array = first_array.filter( (element) => second_array.includes(element));

console.log("Array obtained is :"); console.log(new_array);

`

**Output:

Array obtained is :
[ 3, 5, 9 ]

**Approach 3:

• In this approach, we will look into another approach which is the usage of Set in JavaScript.
• Here, we will convert our two arrays into the sets and then use simple one for-loop and one if-statement. We will check the values of the two sets themselves and then similar values will be pushed into the new array itself.
• That new array will be returned from a function and will be printed in the browser's console as output.

**Example:

JavaScript `

let res_arr = (arr1, arr2) => { let first_array_set = new Set(arr1); let second_array_set = new Set(arr2); let new_array = []; for (let element of second_array_set) { if (first_array_set.has(element)) { new_array.push(element); } } return new_array; };

let first_array = [1, 3, 5, 7, 9]; let second_array = [2, 3, 4, 5, 6, 9];

console.log("Array obtained is: "); console.log(res_arr(first_array, second_array));

`

**Output:

Array obtained is:
[ 3, 5, 9 ]

Using reduce Method

Using the reduce method, iterate through one array, adding elements that are present in both arrays to a new array. Check for element inclusion in the second array using the includes method, effectively creating an array representing their intersection.

**Example: In this example we finds the intersection of two arrays, arr1 and arr2, using the reduce method. It checks if each element in arr1 exists in arr2, collecting common elements into the intersection array.

JavaScript `

let arr1 = [1, 2, 3, 4]; let arr2 = [3, 4, 5, 6];

let intersection = arr1.reduce((acc, curr) => { if (arr2.includes(curr)) { acc.push(curr); } return acc; }, []);

console.log(intersection);

`