30-seconds-of-code/snippets/stable-sort.md

title, tags, cover, firstSeen, lastUpdated

title	tags	cover	firstSeen	lastUpdated
Stable sort	array	horse-sunset	2018-02-06T18:33:49+02:00	2020-10-22T20:24:30+03:00

Performs stable sorting of an array, preserving the initial indexes of items when their values are the same.

• Use Array.prototype.map() to pair each element of the input array with its corresponding index.
• Use Array.prototype.sort() and a compare function to sort the list, preserving their initial order if the items compared are equal.
• Use Array.prototype.map() to convert back to the initial array items.
• Does not mutate the original array, but returns a new array instead.

const stableSort = (arr, compare) =>
  arr
    .map((item, index) => ({ item, index }))
    .sort((a, b) => compare(a.item, b.item) || a.index - b.index)
    .map(({ item }) => item);

const arr = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
const stable = stableSort(arr, () => 0); // [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]