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

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!

Answer

  • 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

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