Replace in array using lodash

Question

Is there an easy way to replace all appearances of an primitive in an array with another one. So that ['a', 'b', 'a', 'c'] would become ['x', 'b', 'x', 'c'] when replacing a with x. I'm aware that this can be done with a map function, but I wonder if have overlooked a simpler way.

I think the purpose of a library like Lo-Dash is not to enable you to write the most code-golfy solution you can possibly write, but to write the most natural and idiomatic solution. And what could be more natural and idiomatic than `map()` in this case? It's the *perfect* tool for the job. — Tomalak, Nov 08 '13 at 14:46
@Tomalak `_(array).filter('someKey').replace('a', 'x')` looks very natural to me — Andreas Köberle, Nov 08 '13 at 14:57
But that would not be logical - I would expect an operation named "filter" to reduce number of elements in the input. Also: It's not about the looks. It's about the *operation* you want to perform on the data, and to me that is "mapping a list of N values a list of N values (some of which by accident happen to be the same as the input)". — Tomalak, Nov 08 '13 at 15:08
Use findIndex from Lodash then replace the element at the found index — Gibrahh, Mar 09 '19 at 07:23

Benjamin Gruenbaum · Answer 1 · 2017-01-11T21:12:10.573

11

In the specific case of strings your example has, you can do it natively with:

myArr.join(",").replace(/a/g,"x").split(",");

Where "," is some string that doesn't appear in the array.

That said, I don't see the issue with a _.map - it sounds like the better approach since this is in fact what you're doing. You're mapping the array to itself with the value replaced.

_.map(myArr,function(el){
     return (el==='a') ? 'x' : el;
})

edited Jan 11 '17 at 21:12

answered Nov 08 '13 at 13:21

Benjamin Gruenbaum

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The question was about primitives not just strings. Also I want to use lodash, as this will be one step in a longer chain, where the array data is manipulated in. – Andreas Köberle Nov 08 '13 at 13:23
@AndreasKöberle First of all using a particular library is a mean and not a goal. Second of all - in that case `_.map` is what you're looking for, underscore/lodash has no specific replace/swap functionality on collections, you can add it to the lodash prototype yourself if you'd like. – Benjamin Gruenbaum Nov 08 '13 at 13:26
2

_.map is really fit to this use case, there's no need to look for anything else. – Denys Séguret Nov 12 '13 at 07:56

score 3 · Answer 2 · answered Nov 08 '13 at 15:08

3

I don't know about "simpler", but you can make it reusable

function swap(ref, replacement, input) {
    return (ref === input) ? replacement : input;
}

var a = ['a', 'b', 'a', 'c'];

_.map(a, _.partial(swap, 'a', 'x'));

answered Nov 08 '13 at 15:08

Tomalak

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score 3 · Answer 3 · edited Jul 22 '21 at 13:42

3

If the array contains mutable objects, It's straightforward with lodash's find function.

  var arr = [{'a':'a'}, {'b':'b'},{'a':'a'},{'c':'c'}];    

  while(_.find(arr, {'a':'a'})){
    (_.find(arr, {'a':'a'})).a = 'x';
  }


console.log(arr); // [{'a':'x'}, {'b':'b'},{'a':'x'},{'c':'c'}]

edited Jul 22 '21 at 13:42

user1677163

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answered Jun 08 '16 at 17:23

j1s

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score 1 · Answer 4 · answered Sep 03 '18 at 20:48

1

Another simple solution. Works well with arrays of strings, replaces all the occurrences, reads well.

var arr1 = ['a', 'b', 'a', 'c'];
var arr2 = _.map(arr1, _.partial(_.replace, _, 'a', 'd'));
console.log(arr2); // ["d", "b", "d", "c"]

answered Sep 03 '18 at 20:48

Ihor

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score 0 · Answer 5 · answered May 09 '23 at 11:37

A replace method like this one could work:

const replacer = (contextArray, itemToReplace, replaceWith) => _.map(
  contextArray,
  (n) => n === itemToReplace ? replaceWith : n
)
console.log(replacer(['a', 'b', 'a', 'c'], "a", "x"))

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.19/lodash.min.js"></script>

Replace in array using lodash

5 Answers5

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