Using JS to convert JSON object key : value pairs to summarised JSON of values

Question

I am using JavaScript and currently I have

filteredObj = 
    [{Amount: 100, Country: "England"},
    {Amount: 100, Country: "England"},
    {Amount: 200, Country: "England"},
    {Amount: 300, Country: "China"},
    {Amount: 200, Country: "China"},
    {Amount: 100, Country: "England"},
    {Amount: 400, Country: "England"},
    {Amount: 300, Country: "China"}]

How can I convert this to

   condensedObj =  [{China: 800,
                     England: 900}]

The following combines the code but keeps them in separate {}s i.e.

 condensedObj = 
[{Country: "China",
  Amount:  800},
  {country: "England",
   Amount: 900}]

Current code:

condensedObj = filteredObj
    .reduce(
      function (res, obj) {
        if (!(obj['Country'] in res))
          res.__array.push(
            (res[obj['Country'] = obj)
          );
        else {
          res[obj['Country'].Amount +=
            obj.Amount;
        }
        return res;
      },
      { __array: [] }
    )
    .__array.sort(function (a, b) {
      return b.Amount - a.Amount;
    });

Thanks!

Show us what you have tried. SO isn't a free code writing service. The objective here is for you to post your attempts to solve your own issue and others help when they don't work as expected. See How to Ask and minimal reproducible example — charlietfl
– charlietfl, Commented Mar 7, 2021 at 15:52

Majed Badawi · Accepted Answer · 2021-03-07 16:21:09Z

1

You can use .reduce to create an object with Country as keys and the sum of Amount as values
Then, sort these pairs according to the value (Amount) as follows:

const arr = [
  { Amount: 100, Country: "England" },
  { Amount: 100, Country: "England" },
  { Amount: 200, Country: "England" },
  { Amount: 300, Country: "China" },
  { Amount: 200, Country: "China" },
  { Amount: 100, Country: "England" },
  { Amount: 400, Country: "England" },
  { Amount: 300, Country: "China" }
];

const countries = arr.reduce((acc, {Amount,Country}) => 
  ({ ...acc, [Country]: (acc[Country] || 0) + Amount })
, {});
const sorted = Object.fromEntries(
  Object.entries(countries).sort(([,amountA],[,amountB]) => amountA - amountB)
);
const res = [ sorted ];

console.log(res);

References:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/Reduce

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/entries

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/fromEntries

edited Mar 7, 2021 at 16:21

answered Mar 7, 2021 at 15:56

Majed Badawi

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4 Comments

user9805590 Over a year ago

Best solution, IMO no other Array method will be more appropriate.

ewldh20 Over a year ago

Thanks very much for this - and sorry about not posting code at start. I have amended the question now but don't want to mark as the solution just yet as this solves for the interim steps from my wrongly outputted JSON to the correctly desired JSON which might confuse people.

Majed Badawi Over a year ago

@ewldh20 I updated the answer with the new specifications

ewldh20 Over a year ago

Thanks very much - I have marked it as working :)

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