Map and Reduce JSON Objects with JavaScript

I tried to do with better time complexity:

let ans = [];
let map = new Map();
ques.cells.forEach(x => {
if(map[x.geo__name]){
map.set(x.geo__name, map[x.geo__name] + x.gdp_growth__avg);
}else{
map.set(x.geo__name,x.gdp_growth__avg);
}
});

map.forEach((v,k)=>{
ans.push({"geo__name":k, "gdp_growth__avg":v});
});
ques.cells = ans;

with solution looking like this:

[
  {
    "geo__name": "united states of america",
    "gdp_growth__avg": 3.79848988541973
  },
  {
    "geo__name": "china",
    "gdp_growth__avg": 10.0085233990531
  },
  {
    "geo__name": "russia",
    "gdp_growth__avg": -4.14352840666389
  },
  {
    "geo__name": "botswana",
    "gdp_growth__avg": -8.66854034194856
  }
]

The Array.reduce method doesn't change the array object, it returns the results in a new array.

Try this:

var data = { cells:[...] };

var r = data.cells.reduce(function(pv, cv) {
    if ( pv[cv.geo__name] ) {
        pv[cv.geo__name] += cv.gdp_growth__avg;
    } else {
        pv[cv.geo__name] = cv.gdp_growth__avg;
    }
    return pv;
}, {});

console.log(r);

Output example:

    { 
      'united states of america': 18.76051995774611,
      'china': 71.39814330096999,
      'russia': -36.291297610751,
      'botswana': -8.730754563729707 
   }