Diff Arrays

Simple utility to diff arrays. Handles arrays of primitives (e.g. strings, numbers) as well as arrays of objects. Can compute a simple difference or a symmetric difference (more on this below).

Install

npm install @mmckelvy/diff-arrays

Usage

Compute a simple difference:

const diffArrays = require('@mmckelvy/diff-arrays');

const diffed = diffArrays([1, 2, 3], [2, 3, 4]);
console.log(diffed); // [1]

Compute a symmetric difference:

const diffed = diffArrays([1, 2, 3], [2, 3, 4], {symmetric: true});
console.log(diffed); // [1, 4]

Works with arrays of objects. Just pass the key on which you want to diff:

const arr1 = [
  {id: 1, name: 'Joe'},
  {id: 2, name: 'Bill'},
  {id: 3, name: 'Jane'},
];

const arr2 = [
  {id: 2, name: 'Bill'},
  {id: 3, name: 'Jane'},
  {id: 4, name: 'Linda'},
];

const diffed = diffArrays(arr1, arr2, {key: 'id', symmetric: true});
console.log(diffed); // [{id: 1, name: 'Joe'}, {id: 4, name: 'Linda'}];

Diffing mechanics and symmetric difference

When diffing two arrays, order matters. Suppose we have two arrays:

const a = [1, 2, 3];
const b = [2, 3, 4];

diffArrays(a, b) will return [1], while diffArrays(b, a) will return [4]. Why? Because in the first case, we are asking "what is in array a that is not in array b?, while in the second case, we are asking "what is in array b that is not in array a?

If you are looking for the answer to both questions, you are looking for the symmetric difference: "what is in array a that is not in array b and what is in array b that is not in array a." To get the symmetric difference with diffArrays, pass {symmetric: true} in the options object.

API

diffArrays(arr1, arr2, options)

arr1 and arr2 can be arrays of primitives or objects. If you pass arrays of objects, include the key you want to use for the diff in the options argument: {key: 'someKey}. Returns an array with the diffed elements.

• arr1 {string[] | number[] | Object[]}
• arr2 {string[] | number[] | Object[]}
• options {Object}
• options.key {string} - The key to use to diff an array of objects.
• options.symmetric {boolean} - Perform a symmetric diff.

Returns {string[] | number[] | Object[]}

Testing

This module uses ava for testing. To run the tests, make sure the dev dependencies are installed and then run:

npm test

License

MIT