unionBy (Lodash Compatibility)

Use unionBy from es-toolkit

This unionBy function operates slowly due to complex processing.

Instead, use the faster and more modern unionBy from es-toolkit.

Merges multiple arrays and keeps only unique values based on a specified criterion.

const result = unionBy(...arrays, iteratee);

Reference

unionBy(...arrays, iteratee)

Use unionBy when you want to merge multiple arrays and remove duplicates based on a given criterion function to create a new array containing only unique values. The order of first appearance of each value is preserved.

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

// Compare by flooring decimal numbers
unionBy([2.1], [1.2, 2.3], Math.floor);
// Returns: [2.1, 1.2]

// Compare by object property
unionBy([{ x: 1 }], [{ x: 2 }, { x: 1 }], 'x');
// Returns: [{ x: 1 }, { x: 2 }]

// Compare with function
unionBy(
  [{ id: 1, name: 'a' }],
  [
    { id: 2, name: 'b' },
    { id: 1, name: 'c' },
  ],
  item => item.id
);
// Returns: [{ id: 1, name: 'a' }, { id: 2, name: 'b' }]

// Compare with partial object
unionBy([{ x: 1, y: 1 }], [{ x: 1, y: 2 }], { x: 1 });
// Returns: [{ x: 1, y: 1 }]

null or undefined arrays are ignored.

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

unionBy([1, 2], null, undefined, [3, 4], x => x);
// Returns: [1, 2, 3, 4]

Parameters

• ...arrays (Array<ArrayLike<T> | null | undefined>): The arrays to merge.
• iteratee (ValueIteratee<T>): The criterion to determine uniqueness. Can be a function, property name, partial object, or property-value array.

Returns

(T[]): Returns a new array containing unique values with duplicates removed based on the specified criterion.