lodash: mapping array to object

Question

Is there a built-in lodash function to take this:

var params = [
    { name: 'foo', input: 'bar' },
    { name: 'baz', input: 'zle' }
];

And output this:

var output = {
    foo: 'bar',
    baz: 'zle'
};

Right now I'm just using Array.prototype.reduce():

function toHash(array, keyName, valueName) {
    return array.reduce(function(dictionary, next) {
        dictionary[next[keyName]] = next[valueName];
        return dictionary;
    }, {});
}

toHash(params, 'name', 'input');

Wondering if there's a lodash short-cut.

Mustafa Ehsan Alokozay · Accepted Answer · 2019-10-19 09:41:41Z

211

Another way with lodash 4.17.2

_.chain(params)
    .keyBy('name')
    .mapValues('input')
    .value();

or

_.mapValues(_.keyBy(params, 'name'), 'input')

or with _.reduce

_.reduce(
    params,
    (acc, { name, input }) => ({ ...acc, [name]: input }),
    {}
)

edited Oct 19, 2019 at 9:41

Mustafa Ehsan Alokozay

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answered Dec 7, 2016 at 14:08

stasovlas

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5 Comments

Mustafa Ehsan Alokozay Over a year ago

@Akrikos the _.keyBy will transform the entire array to an object, whereas the question is mostly about having one item from each object in array as key and one other item as its value. If _.keyBy is used, then all values will be objects.

Akrikos Over a year ago

Thanks @MustafaEhsanAlokozay You're right, that answer does not do the exact right thing. I'll delete my comment as it's not helpful. That may make your comment look weird, but better that than have my incorrect comment stay up any longer.

vilem cech Over a year ago

Anyone knows how to make this work with Typescript? is there a way to get object of output type with lodash?

Frexuz Over a year ago

For reduce, just use es6, zero point in lodash for this case. For Typescript, just put in the resulting type balances.reduce<Record<string, AccountBalanceValue>>

nightwuffle Over a year ago

@vilemcech You'll have to cast the accumulator dictionary to get Typescript to be happy. For this example, it would be: {} as { [key: string]: string }.

danday74 · Accepted Answer · 2017-11-21 15:51:20Z

97

You should be using _.keyBy to easily convert an array to an object.

Docs here

Example usage below:

var params = [
    { name: 'foo', input: 'bar' },
    { name: 'baz', input: 'zle' }
];
console.log(_.keyBy(params, 'name'));

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.4/lodash.min.js"></script>

If required, you can manipulate the array before using _.keyBy or the object after using _.keyBy to get the exact desired result.

answered Nov 21, 2017 at 15:51

danday74

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4 Comments

Roman Susi Over a year ago

Look first at this to understand most voted answer by stasovlas.

Pilaf T. Pilafian Over a year ago

This is a cool answer, but it does NOT answer the question. The values should be strings not objects.

sf8193 Over a year ago

is there a way to have it not convert key into string?

Manuel Astudillo Over a year ago

This does not answer the question since it does not return what is asked, namely: { foo: 'baz', baz: 'zle' }

Jagdish Idhate · Accepted Answer · 2016-02-18 19:27:09Z

44

Yep it is here, using _.reduce

var params = [
    { name: 'foo', input: 'bar' },
    { name: 'baz', input: 'zle' }
];

_.reduce(params , function(obj,param) {
 obj[param.name] = param.input
 return obj;
}, {});

edited Feb 18, 2016 at 19:27

answered Feb 18, 2016 at 18:57

Jagdish Idhate

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3 Comments

Dan Over a year ago

Yet again reduce() swoops in with another use case. Smart way of doing it!

mr.bjerre Over a year ago

Anyone got the typescripted version of this?

Robert Fischer Over a year ago

The reality is that's mathematically true that you can implement literally any iteration action using reduce/inject, since reduce is isomorphic to a list. However, that flexibility comes with a price in readability. Don't use _.reduce unless that accurately expresses what you're trying to do: it significantly obscures the point of the code in any other case. I personally prefer the _.zipObject solution by @djechlin -- failing that, the _.keyBy/_.mapValues approach.

RainedColony · Accepted Answer · 2019-01-30 21:45:26Z

26

This seems like a job for Object.assign:

const output = Object.assign({}, ...params.map(p => ({[p.name]: p.input})));

Edited to wrap as a function similar to OP's, this would be:

const toHash = (array, keyName, valueName) => 
    Object.assign({}, ...array.map(o => ({[o[keyName]]: o[valueName]})));

(Thanks to Ben Steward, good thinking...)

edited Jan 30, 2019 at 21:45

answered Jan 30, 2019 at 20:12

RainedColony

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2 Comments

Ben Steward Over a year ago

Maybe wrap that in a parent function so the user can determine what keys would be used by passing them, like the OP had.

utopia Over a year ago

Thank you. This works well also if you want the value to be something else than input. For example, a boolean

peterjwest · Accepted Answer · 2023-10-04 15:34:03Z

16

This is probably more verbose than you want, but you're asking for a slightly complex operation so actual code might be involved (the horror).

My recommendation, with zipObject that's pretty logical:

_.zipObject(_.map(params, 'name'), _.map(params, 'input'));

Another option, more hacky, using fromPairs:

_.fromPairs(_.map(params, function(val) { return [val['name'], val['input']));

The anonymous function shows the hackiness -- I don't believe JS guarantees order of elements in object iteration, so callling .values() won't do.

edited Oct 4, 2023 at 15:34

peterjwest

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answered Feb 18, 2016 at 19:28

djechlin

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1 Comment

x-yuri Over a year ago

I don't see anything hacky about using fromPairs, and calling values() indeed won't do. At least from readability standpoint.

Faisal Hasnain · Accepted Answer · 2018-03-16 10:36:32Z

12

You can use one liner javascript with array reduce method and ES6 destructuring to convert array of key value pairs to object.

arr.reduce((map, { name, input }) => ({ ...map, [name]: input }), {});

answered Mar 16, 2018 at 10:36

Faisal Hasnain

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3 Comments

jimrandomh Over a year ago

Unfortunately, this is O(n^2).

Mizanur Rahman Mojumder Over a year ago

arr.reduce((map, { name, input }) => (map[name] = input, map), {}); @jimrandomh what about this?

jimrandomh Over a year ago

That version is O(n), but it modifies its input, which is something you usually don't want. I think for this sort of thing, it's generally better to write a full-length utility function with a foreach loop, put it in a utils folder out of the way somewhere and import it, rather than trying to be clever with one-liners.

Koushik Chatterjee · Accepted Answer · 2017-12-07 10:31:34Z

8

Another way with lodash

creating pairs, and then either construct a object or ES6 Map easily

_(params).map(v=>[v.name, v.input]).fromPairs().value()

or

_.fromPairs(params.map(v=>[v.name, v.input]))

Here is a working example

var params = [
    { name: 'foo', input: 'bar' },
    { name: 'baz', input: 'zle' }
];

var obj = _(params).map(v=>[v.name, v.input]).fromPairs().value();

console.log(obj);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.4/lodash.js"></script>

answered Dec 7, 2017 at 10:31

Koushik Chatterjee

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2 Comments

fregante Over a year ago

The good part of this solution is that it's also feasible in plain ES: Object.fromEntries(params.map(v => [v.name, v.input]))

d9k Over a year ago

@fregante, Chrome 73+ only caniuse.com/?search=fromEntries

Zeeshan Afzal Satti · Accepted Answer · 2018-03-16 10:49:53Z

7

It can also solve without using any lodash function like this:

let paramsVal = [
    { name: 'foo', input: 'bar' },
    { name: 'baz', input: 'zle' }
];
let output = {};

paramsVal.forEach(({name, input})=>{
  output[name] = input;
})


console.log(output);

answered Mar 16, 2018 at 10:49

Zeeshan Afzal Satti

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