Add third key to array of objects summing up values of second key-CodePudding

I know this might be an easy task though I am struggling quite a lot with this one:

I have an Array of objects looking like this:

[{date: '01-01-2022' , count: 1},
 {date: '02-01-2022' , count: 2},
 {date: '05-01-2022' , count: 9}]

My expected outcome would be:

[{date: '01-01-2022' , count: 1 , sum: 1},
 {date: '02-01-2022' , count: 2 , sum: 3},
 {date: '05-01-2022' , count: 9 , sum: 12}]

or alternatively:

[{date: '01-01-2022' , count: 1},
 {date: '02-01-2022' , count: 3},
 {date: '05-01-2022' , count: 12}]

I can sum up the count array using

    let new_array = [];  
    myarray.reduce( (prev, curr,i) =>  new_array[i] = prev   curr , 0 )
    return (new_array);

but I never manage to let it happen in the original array of objects or adding the thing to the original array of objects.

Thank you in advance!

CodePudding user response：

If you want to mutate the original array don't create a new one (let new_array = [];), simply iterate over the original and add the property you want to each object.

const input = [{ date: '01-01-2022', count: 1 }, { date: '02-01-2022', count: 2 }, { date: '05-01-2022', count: 9 }]

let sum = 0;
for (const o of input) {
  o.sum = (sum  = o.count);
}

console.log(input);

CodePudding user response：

Here's something that would work for your case since you want to do it in original array of objects:

let myArray = [{date: '01-01-2022' , count: 1},
 {date: '02-01-2022' , count: 2},
 {date: '05-01-2022' , count: 9}];

myArray.map((entry, index, arr) => {
    entry.sum = index? arr[index-1].sum   entry.count : entry.count;
    delete entry.count; // Provides alternative outcome, remove for expected outcome
    return entry;
});

console.log(myArray);

CodePudding user response：

we can achieve by map also

   

 

const input = [{ date: '01-01-2022', count: 1 },{ date: '02-01-2022', count: 2 },{ date: '05-01-2022', count: 9 }]

const fun = (ar)=>{
  var t = 0
  const get = ar.map((e, i)=> {
    t = t e.count
    const Data = {date : e.date,count : e.count,sum : t}
    return Data
})
  return get
}
console.log(fun(input))