JavaScript Reduce Array of objects to object dictionary

Question

I've read this answer on SO to try and understand where I'm going wrong, but not quite getting there.

I have this function :

get() {
    var result = {};

    this.filters.forEach(filter => result[filter.name] = filter.value);

    return result;
}

It turns this :

[
    { name: "Some", value: "20160608" }
]

To this :

{ Some: "20160608" }

And I thought, that is exactly what reduce is for, I have an array, and I want one single value at the end of it.

So I thought this :

this.filters.reduce((result, filter) => {
    result[filter.name] = filter.value;
    return result;
});

But that doesn't produce the correct result.

1) Can I use Reduce here?

2) Why does it not produce the correct result.

From my understanding, the first iteration the result would be an empty object of some description, but it is the array itself.

So how would you go about redefining that on the first iteration - these thoughts provoke the feeling that it isn't right in this situation!

This is not a filter job. If you want to receive a dictionary object it must be done by reduce. Try @Pranav C Balan's answer. — Redu
– Redu, Commented Jun 8, 2016 at 15:20
@Redu They aren't using filter. They have an array named filters but they're performing a reduce on that array. — Mike Cluck
– Mike Cluck, Commented Jun 8, 2016 at 15:50
@Redu I know. Read the code. They aren't using filter. It's a forEach which is being used like reduce. — Mike Cluck
– Mike Cluck, Commented Jun 8, 2016 at 15:58

Pranav C Balan · Accepted Answer · 2016-06-08 15:41:11Z

37

Set initial value as object

this.filters = this.filters.reduce((result, filter) => {
    result[filter.name] = filter.value;
    return result;
},{});
//-^----------- here

var filters = [{
  name: "Some",
  value: "20160608"
}];

filters = filters.reduce((result, filter) => {
  result[filter.name] = filter.value;
  return result;
}, {});

console.log(filters);

var filters = [{
  name: "Some",
  value: "20160608"
}];

filters = filters.reduce((result, {name, value}= filter) => (result[name] = value, result), {});

console.log(filters);

edited Jun 8, 2016 at 15:41

answered Jun 8, 2016 at 15:13

Pranav C Balan

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4 Comments

ssube Over a year ago

You could also use parameter destructuring to shorten this a bit: (result, {name, value} = filter) => (result[name] = value, result)

Callum Linington Over a year ago

That doesn't give me the output I'm expecting... could you do it in plnkr or something?

Pranav C Balan Over a year ago

@CallumLinington : check the snippets added

Callum Linington Over a year ago

Wait one minute, I didn't see that last parameter you supplied to the reduce function.. And I completely missed that when reading the MDN docs. I might as well, delete the question ....

Ondra · Accepted Answer · 2022-09-26 13:59:06Z

2

Since 2019 (ES2019) you can go with Object.fromEntries() but you need to map to array first.

const filtersObject = Object.fromEntries(filters.map(({ name, value }) => [name, value])

answered Sep 26, 2022 at 13:59

Ondra

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