Group By and Sum using Underscore/Lodash

Question

I have JSON like this:

[
  {
     platformId: 1,
     payout: 15,
     numOfPeople: 4
  },
  {
     platformId: 1,
     payout: 12,
     numOfPeople: 3

  }         


        

Answer 1

//Input 
[{
  "platformId": 1,
  "payout": 15,
  "numOfPeople": 4
}, {
  "platformId": 1,
  "payout": 12,
  "numOfPeople": 3
}, {
  "platformId": 2,
  "payout": 6,
  "numOfPeople": 5
}, {
  "platformId": 2,
  "payout": 10,
  "numOfPeople": 1
}]


//Output
{
 "1": {
    "payout": 43,
    "numOfPeople": 13
 },
 "2": {
    "payout": 43,
    "numOfPeople": 13
 }
}


// Code
output = _.reduce(input, function(acc, val, key) {
  acc[val.platformId] = {
     payout: _.sum(a, 'payout'),
     numOfPeople: _.sum(a, 'numOfPeople')
   };
  return acc;
  }, {});