Support for replacement in array #1967

jfmengels · 2016-02-09T18:20:50Z

I am often (in multiple projects) reimplementing the same utility function, that replaces a value in an array based on some condition (a position or a field is equal to X), without mutating the original array (like map in that regard):

array.map(function(value) {
  if (value.id !== ID) {
    return value;
  }
  return REPLACEMENT;
});

array.map(function(value, index) {
  if (index !== POSITION) {
    return value;
  }
  return REPLACEMENT;
});

I would like to dip my toe in the water and see if others would be interested in having a function that does this.

/**
 * Replace a value in `array` when `condition` matches.
 * 
 * @param {Array} array The collection to iterate over.
 * @param {Function|number|Object} condition Condition to match.
 * @param {*} iteratee The function invoked if `condition` matches, or the replacement value.
 * @return {Array} Returns the new mapped array.
 */
function mapReplace(array, condition, iteratee) {
  // ...
}

// Mapped in lodash/fp ([2, 0, 1])
_.mapReplace(condition, iteratee, array);

Example

function plusTen(x) {
  return x + 10;
}

function isEven(x) {
  return x % 2 === 0;
}

var array = [0, 1, 2, 3];

// Using index as condition and simple value as iteratee ( = replacement)
_.mapReplace(array, 2, 'replacement');
// => [0, 1, 'replacement', 3]

// Using index as condition and function as iteratee
_.mapReplace(array, 2, plusTen);
// => [0, 1, 12, 3]

// Using function as condition and function as iteratee
_.mapReplace(array, isEven, plusTen);
// => [10, 1, 12, 3]
// or if it is only applied to the first found element, and a mapReplaceAll exists:
// => [10, 1, 2, 3]

// Using object to get field as condition and value as iteratee
_.mapReplace([{id: 0, val: 0}, {id: 1, val: 1}], {id: 1}, {id: 1, foo: 'bar'});
// => [{id: 0, val: 0}, {id: 1, foo: 'bar'}]

I would have liked it to be named replace, but since that is already taken... ^^'
I used mapReplace in the example but open to suggestions.

I'd argue it would be nice to have one function to update the first found item, and one to update them all (kind of like the proposal for replaceAll).

The text was updated successfully, but these errors were encountered:

jdalton · 2016-02-09T18:30:23Z

Thanks @jfmengels!

We'll keep an eye on the popularity of the request.

Side note:
I'd make the signature (array, condition, iteratee) to align closer to _.replace.

jfmengels · 2016-02-09T19:20:41Z

Agreed on the signature (updated it), it's what I was using in the examples actually.

slorber · 2016-02-25T13:38:17Z

+1 for this feature

I'd also find it useful to have the possibility to add multiple elements at a given array index (immutable splice)

Gaafar · 2016-07-04T08:47:37Z

This would be really useful in reactjs to update an array in the state. +1

EthanLin-TWer · 2018-02-21T07:03:22Z

+1 for this feature. In our cases we need to maintain an array(or could be an object) of the app's tabs status in Redux like this:

const initialState = Immutable.from({
  selected: [ 
    { page: Pages.NEWS, active: true, tabs: [
      { tab: Tabs.HOTTEST, active: false, subTabs: []}, 
      { tab: Tabs.HISTORY, active: true, subTabs: []},
      { tab: Tabs.RECOMMENDATIONS, active: false, subTabs: []},
    ]},
    { page: Pages.VIDEOS, active: false, tabs: []},
  ],
})

While an updateActiveTab(Pages.NEWS, Tabs.HOTTEST) action is dispatched, we'd like to update the 'hottest' tab under the news page as active: true and others(history news and recommendations) as active: false. In this case the proposed mapReplace function will definitely help.

Using other data structure might help in our case but I'm just posting the possible situation we've been met where mapReplace would make life easier.

gablabelle · 2019-10-19T17:46:57Z

Hello guys, so I was curious... Is it currently possible to do something like this in lodash? Or we still have to use our own util function across projects (basic example):

const updateArray = (list, updatedItem) => {
   const index = list.findIndex(item => item.id === updatedItem.id);
   return [
    ...list.slice(0, index),
    ...updatedItem,
    ...list.slice(index + 1)
   ];
}

Because what's the process? Suggestions are made, tags like enhancement and votes needed are added to the issue and then the issue gets closed, then what?

StarScape · 2020-05-01T22:10:26Z

Bump. I find myself needing this a lot and would very much like to see this feature.

riotrah · 2022-03-24T23:00:41Z

Hi, please forgive if "bump+1" comments on issues is the wrong kind of vote (per your docs), and do not want to appear entitled, but am not sure anyways given the radio silence - so I'm adding both. Apologies if my doing so on several diff issues constitutes spam ( I genuinely am not sure and not intending it to be! )

jdalton added enhancement wontfix labels Feb 9, 2016

jdalton closed this as completed Feb 9, 2016

jfmengels mentioned this issue Feb 25, 2016

Update array element at index #2053

Closed

jdalton added votes needed and removed wontfix labels Apr 13, 2016

jfmengels mentioned this issue May 10, 2016
8000

_.replace(collection, match, new) #1022

Closed

nicksellen mentioned this issue Jan 19, 2020

Migrate Tribes page to React (finishing the feature) Trustroots/trustroots#1145

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Support for replacement in array #1967

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