Add object key to each item in object array

Question

I have a payload coming back from an endpoint like this:

const charges = [
    {
        'id': 'someId',
        'dates': ['2017-11-11', '2017-12-11'],
    },
    {
        'id': 'anotherId',
        'dates': ['2017-09-11', '2017-10-11'],
    },
];

What would be the best way to attach id to each of the items in the dates array so that it results in this:

[
    { id: 'someId', date: '2017-11-11' },
    { id: 'someId', date: '2017-12-11' },
    { id: 'anotherId', date: '2017-09-11' },
    { id: 'anotherId', date: '2017-10-11' },
]

I've tried something like this:

let history = [];
charges.map(charge => (
    charge.dates.map((date) => (
        history.concat({
            id: charge.payerCode,
            date: date,
        })
    ))
));

But history is not defined in the scope I'm using it in.

I know there is probably a better way to do this, but I just can't seem to wrap my head around it.

Any help would be greatly appreciated!

Thanks!

Are you trying to make history contain your desired output? — castletheperson
– castletheperson, Commented Aug 8, 2017 at 12:50
map isn't the right tool here as your output array won't possibly have the same number of elements than your input array. reduce is the tool to use, as proposed in the answers. — sp00m
– sp00m, Commented Aug 8, 2017 at 12:54

Nina Scholz · Accepted Answer · 2017-08-08 13:29:16Z

You could Array#reduce while concat all objects, build with dates arrays.

let charges = [{ id: 'someId', dates: ['2017-11-11', '2017-12-11'] }, { id: 'anotherId', dates: ['2017-09-11', '2017-10-11'] }],
    result = charges.reduce((r, { id, dates }) => r.concat(dates.map(date => ({ id, date }))), []);

console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

Edge version, which prevents (it might be a bug inside of Edge)

SCRIPT5113: Use before declaration
result = charges.reduce((r, { id, dates }) => r.concat(dates.map(date => ({ id, date }))), []);
                                                                            ^

const
    charges = [{ id: 'someId', dates: ['2017-11-11', '2017-12-11'] }, { id: 'anotherId', dates: ['2017-09-11', '2017-10-11'] }],
    result = charges.reduce((r, a) => r.concat(a.dates.map(d => ({ id: a.id, date: d }))), []);

console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

Ben Aston · Accepted Answer · 2017-08-08 12:56:20Z

3

const charges = [
    {
        'id': 'someId',
        'dates': ['2017-11-11', '2017-12-11'],
    },
    {
        'id': 'anotherId',
        'dates': ['2017-09-11', '2017-10-11'],
    },
];

function flatten(charges) {    
  return charges.reduce((p, {id, dates}) => 
           (dates.forEach(date => p.push({id, date})), p), []);    
}

console.log(flatten(charges))

answered Aug 8, 2017 at 12:56

Ben Aston

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Comments

abhishekkannojia · Accepted Answer · 2017-08-08 12:50:09Z

1

You can use Array#reduce in combination with Array#concat like this :

const charges = [
    {
        'id': 'someId',
        'dates': ['2017-11-11', '2017-12-11'],
    },
    {
        'id': 'anotherId',
        'dates': ['2017-09-11', '2017-10-11'],
    },
];

var r = charges.reduce(function(acc, obj) {
  return acc.concat(obj.dates.map(function(date) {
    return {
      id : obj.id,
      date : date
    };
  }))
}, []);

console.log(r);

answered Aug 8, 2017 at 12:50

abhishekkannojia

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Comments

castletheperson · Accepted Answer · 2017-08-08 12:53:41Z

1

A simple imperative solution would be:

const history = [];
for (const { payerCode, dates } of charges) {
  for (const date of dates) {
    history.push({ id: payerCode, date });
  }
}

answered Aug 8, 2017 at 12:53

castletheperson

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Comments

Nofi · Accepted Answer · 2017-08-08 12:55:29Z

0

$(document).ready(function(){
    const charges = [
    {
        'id': 'someId',
        'dates': ['2017-11-11', '2017-12-11'],
    },
    {
        'id': 'anotherId',
        'dates': ['2017-09-11', '2017-10-11'],
    },
];
var temp={};
var finalArray = [];
for(ch in charges){
    for(dt of charges[ch]['dates']){
        temp.id = charges[ch]['id'];
        temp.date =dt;
        finalArray.push(temp);
        temp={};
    }
}
console.log(JSON.stringify(finalArray));
});

answered Aug 8, 2017 at 12:55

Nofi

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Comments

prasanth · Accepted Answer · 2017-08-08 13:06:44Z

0

Try with Array#reduce recreate the array and Array#forEach to iterate the inner array

const charges = [{'id': 'someId', 'dates': ['2017-11-11', '2017-12-11'],}, { 'id': 'anotherId','dates': ['2017-09-11', '2017-10-11'],},];

var res = charges.reduce(function(a,b){
b.dates.forEach(function(n){
a.push({id:b.id,dates:n})
})
return a;
},[])

console.log(res)

ES6

const charges = [{'id': 'someId', 'dates': ['2017-11-11', '2017-12-11'],}, { 'id': 'anotherId','dates': ['2017-09-11', '2017-10-11'],},];

var res = charges.reduce((a,b) =>(b.dates.forEach(d=>a.push({id:b.id,dates:d})),a),[])

console.log(res)

edited Aug 8, 2017 at 13:06

answered Aug 8, 2017 at 12:52

prasanth

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