es-toolkit/docs/reference/array/intersectionBy.md

intersectionBy

Returns the intersection of two arrays based on a mapping function.

This function takes two arrays and a mapping function. It returns a new array containing the elements from the first array that, when mapped using the provided function, have matching mapped elements in the second array. It effectively filters out any elements from the first array that do not have corresponding mapped values in the second array.

Signature

function intersectionBy<T, U>(firstArr: T[], secondArr: T[], mapper: (item: T) => U): T[];

Parameters

• firstArr (T[]): The first array to compare.
• secondArr (T[]): The second array to compare.
• mapper ((item: T) => U): A function to map the elements of both arrays for comparison.

Returns

(T[]) A new array containing the elements from the first array that have corresponding mapped values in the second array.

Examples

const array1 = [{ id: 1 }, { id: 2 }, { id: 3 }];
const array2 = [{ id: 2 }, { id: 4 }];
const mapper = item => item.id;
const result = intersectionBy(array1, array2, mapper);
// result will be [{ id: 2 }] since only this element has a matching id in both arrays.

Lodash Compatibility

Import intersectionBy from es-toolkit/compat for full compatibility with lodash.

• intersectionBy can accept multiple array-like objects to find common elements.
• intersectionBy can accept a property key as the iteratee.

import { intersectionBy } from 'es-toolkit/compat';

const array1 = [1.2, 2.4, 3.6];
const array2 = [2.5, 3.7];
const array3 = [2.6, 3.8];
const result = intersectionBy(array1, array2, array3, Math.floor);
// result will be [2.4, 3.6] since the common elements after applying Math.floor are 2 and 3.

const array1 = [{ x: 1 }, { x: 2 }, { x: 3 }];
const array2 = [{ x: 2 }, { x: 3 }, { x: 4 }];
const result = intersectionBy(array1, array2, 'x');
// result will be [{ x: 2 }, { x: 3 }] since these elements have the same `x` property.

const arrayLike1 = { 0: 'apple', 1: 'banana', 2: 'cherry', length: 3 };
const arrayLike2 = { 0: 'banana', 1: 'cherry', 2: 'date', length: 3 };
const result = intersectionBy(arrayLike1, arrayLike2);
// result will be ['banana', 'cherry'] since these elements are common between the two array-like objects.