transform property value of object using reduce?

Question

const ori = {
    "AL": "Alabama",
    "AK": "Alaska",
    "AS": "American Samoa"
}

How do I concate above array of object into

{
    "AL": "+ Alabama",
    "AK": "+ Alaska",
    "AS": "+ American Samoa"
}

using reduce?

I tried

const r = Object.entries(ori).reduce((accum, [key, value], i) => {
    console.log(key)
    accum = {[key]: `+ ${value}`}

    return accum
},{})
console.log(r)

I only got the last iteration value.

reduce is for arrays, you'd have to convert it first. also reduce is for many->one, and you want many->many, which is a map(). — dandavis
– dandavis, Commented Oct 2, 2018 at 3:48
The first piece of code is only an object, not an array of objects. — Adam
– Adam, Commented Oct 2, 2018 at 3:48
The reason your attempt doesn't work is because you assign the accumulator to an entirely new object each iteration. What you want to do is add new properties to the existing accumulator. — Phil
– Phil, Commented Oct 2, 2018 at 3:54

JLRishe · Accepted Answer · 2018-10-02 03:52:11Z

3

You just need to use the ... operator to combine the current value of accum with the next entry:

const ori = {
    "AL": "Alabama",
    "AK": "Alaska",
    "AS": "American Samoa"
}

const r = Object.entries(ori).reduce((accum, [key, value]) => {
    console.log(key)
    return {...accum, [key]: `+ ${value}`};
},{})
console.log(r)

answered Oct 2, 2018 at 3:52

JLRishe

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5 Comments

Phil Over a year ago

Seems kinda odd to recreate the accumulator each iteration when you could just use return accum[key] = '+ ' + value, accum

JLRishe Over a year ago

@Phil Sure, you could, but part of the idea of functional programming (such as reduce) is avoiding mutability. accum[key] = would mutate the accumulator object. If the number of items is a known commodity and it's small, then the approach above shouldn't be too big of a deal.

Phil Over a year ago

Since the accumulator is created new specifically for the reduce operation, I don't think I've ever seen an issue in mutating it

JLRishe Over a year ago

@Phil No, there's no issue in mutating it. It's simply a matter of whether you want to consistently adhere to immutability or not.

Felix Kling Over a year ago

@Melissa94: ... is not an operator!

Phil · Accepted Answer · 2018-10-02 04:02:26Z

1

transform property value of an object

An alternative for using reduce

Try this:

const obj = {
  "AL": "Alabama",
  "AK": "Alaska",
  "AS": "American Samoa"
}
let clone = {}
for (var propt in obj) {
  clone[propt] = `+ ${obj[propt]}`
}
console.log(clone )

edited Oct 2, 2018 at 4:02

Phil

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answered Oct 2, 2018 at 3:55

Tu Nguyen

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