Web Front-endJS TutorialHow to create an array from the intersection of two arrays in JavaScript?
Intersection of two arrays in JavaScript can be done in different ways, such as using Set, spread operator, filter() method or includes() method. Each method has its own advantages and disadvantages, and it is important to consider which method is best for a given task. The intersection of two arrays can be helpful if you want to create a new array containing only the elements found in both arrays.
Let us give an example -
arr1 = [ 2, 5, 7, 9, 11, 13, 15, 17 ] arr2 = [ 1, 3, 5, 7, 11, 13, 16, 17 ] intersecArr = [ 5, 6, 11, 13, 17 ]
Above we defined two arrays arr1 and arr2, including some of the same values that exist in the two arrays. The intersection of the two arrays is antersecArr.
Let’s discuss ways to create an array from the intersection of two arrays in JavaScript.
Method 1: Use filter() and includes() methods
We can use the filter() and includes() methods to perform intersection on two arrays. The filter() method accepts a function as its argument and applies it to each element in the array. The function should return a Boolean value of true or false indicating whether the element should be included in the new array. In our case, we want the element to be present in both input arrays, so we will use the includes() method to check if the element is present in the other array.
grammar
The following is the syntax for using the filter() and include() methods to create a new array from the intersection of two arrays -
let intersection = arr1.filter(x => arr2.includes(x));
The filter() method accepts a callback function as its parameter. This callback function is applied to each element of the first array (arr1) and uses the includes() method to check if the current element (x) is present in the second array (arr2). If the current element (x) exists in the second array (arr2), it is included in the new array (intersection).
If the current element (x) does not exist in the second array (arr2), exclude it from the new array (intersection). The end result is a new array (the intersection) containing only the elements present in arr1 and arr2.
Example
In the following example, we create two arrays arr1 and arr2, each with five elements, three of which are the same. Then use the filter and contain methods to create a new array of common elements from both arrays.
<html>
<head>
<title>Creating an Array using Intersection of two Arrays using Filter() and Includes() methods</title>
</head>
<body>
<p id="arr1"></p>
<p id="arr2"></p>
<p id="result"></p>
<script>
let arr1 = [5, 6, 8, 11, 15];
let arr2 = [3, 5, 8, 11, 17];
document.getElementById("arr1").innerHTML = "Array 1: " + JSON.stringify(arr1);
document.getElementById("arr2").innerHTML = "Array 1: " + JSON.stringify(arr2);
const intersection = arr1.filter(x => arr2.includes(x));
document.getElementById("result").innerHTML = "Intersection of Array1 & Array 2: " + JSON.stringify(intersection);
</script>
</body>
</html>
The above code will create a new array, intersectionArray, which only contains elements that are present in both input arrays.
Method 2
In this method, we first create a new collection object from the elements of arr1. It removes any duplicate elements. Then use the spread operator to convert the collection object to an array. The array has no duplicate elements. Now we use filter() and include() methods to perform intersection. The further process is the same as the first method.
let intersection = [...new Set(arr1)].filter(x => arr2.includes(x));
The above syntax creates a new array "intersection". After removing all duplicates from arr1, it contains elements present in arr1 and arr2.
Example
Creating an Array using Intersection of two Arrays using Spread Operator and Filter() method <script> let arr1 = [4, 8, 12, 16, 20, 28]; let arr2 = [8, 16, 20, 24, 28, 30]; document.getElementById("arr1").innerHTML = "Array 1: " + JSON.stringify(arr1); document.getElementById("arr2").innerHTML = "Array 1: " + JSON.stringify(arr2); let intersection = [...new Set(arr1)].filter(x => arr2.includes(x)); document.getElementById("result").innerHTML = "Intersection of Array1 & Array 2: " + JSON.stringify(intersection); </script>
Method 3: Using Set
In this method, first, we use the new Set() constructor to convert the array into a set. Then use a for...of loop to iterate over the elements of the second set. Then use the has() method to check if the element is in the first Set. If the element exists in the first Set, use the push() method to add the element to the intersection array.
Example
<html>
<head>
<title>Creating an Array using Intersection of two Arrays using Set</title>
</head>
<body>
<p id="arr1"></p>
<p id="arr2"></p>
<p id="result"></p>
<script>
function doIntersection(arr1, arr2) {
const setFirst = new Set(arr1);
const setSecond = new Set(arr2);
let intersection = [];
for (let i of setSecond) {
if (setFirst.has(i)) {
intersection.push(i);
}
}
return intersection;
}
const arrFirst = [4, 6, 8, 10, 12];
const arrSecond = [4, 5, 8, 12, 15];
document.getElementById("arr1").innerHTML = "Array 1: " + JSON.stringify(arrFirst);
document.getElementById("arr2").innerHTML = "Array 1: " + JSON.stringify(arrSecond);
const interResult = doIntersection(arrFirst, arrSecond);
document.getElementById("result").innerHTML = "Intersection of Array1 & Array 2: " + JSON.stringify(interResult);
</script>
</body>
</html>
In this tutorial, we have discussed three ways to create an array using the intersection of two arrays with the help of examples. In the first method, we use filter() and include() methods, while in the second method, in addition to filter and include, we also use spread operator and Set. In the third approach, we create a custom function to perform this task.
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