Map and Reduce JSON Objects with JavaScript

Question

Consider this JSON object below:

{
   "cells":[
      {
         "count":"1",
         "gdp_growth__avg":1.90575802503285,
         "geo__name":"united states of america",
         "time":1990
      },
      {
         "count":"1",
         "gdp_growth__avg":9.17893670154459,
         "geo__name":"china",
         "time":1991
      },
      {
         "count":"1",
         "gdp_growth__avg":-5.04693945214571,
         "geo__name":"russia",
         "time":1991
      },
      {
         "count":"1",
         "gdp_growth__avg":-0.0622142217811472,
         "geo__name":"botswana",
         "time":1991
      },
      {
         "count":"1",
         "gdp_growth__avg":14.2407063986337,
         "geo__name":"china",
         "time":1992
      },
      {
         "count":"1",
         "gdp_growth__avg":-14.5310737731921,
         "geo__name":"russia",
         "time":1992
      },
      {
         "count":"1",
         "gdp_growth__avg":3.55494453739944,
         "geo__name":"united states of america",
         "time":1992
      },
      {
         "count":"1",
         "gdp_growth__avg":13.9643147001603,
         "geo__name":"china",
         "time":1993
      },
      {
         "count":"1",
         "gdp_growth__avg":-8.66854034194856,
         "geo__name":"botswana",
         "time":1993
      },
      {
         "count":"1",
         "gdp_growth__avg":2.74204850437989,
         "geo__name":"united states of america",
         "time":1993
      },
      {
         "count":"1",
         "gdp_growth__avg":4.04272516401846,
         "geo__name":"united states of america",
         "time":1994
      },
      {
         "count":"1",
         "gdp_growth__avg":13.0806818010789,
         "geo__name":"china",
         "time":1994
      },
      {
         "count":"1",
         "gdp_growth__avg":-12.5697559787493,
         "geo__name":"russia",
         "time":1994
      },
      {
         "count":"1",
         "gdp_growth__avg":10.9249803004994,
         "geo__name":"china",
         "time":1995
      },
      {
         "count":"1",
         "gdp_growth__avg":-4.14352840666389,
         "geo__name":"russia",
         "time":1995
      },
      {
         "count":"1",
         "gdp_growth__avg":2.71655384149574,
         "geo__name":"united states of america",
         "time":1995
      },
      {
         "count":"1",
         "gdp_growth__avg":10.0085233990531,
         "geo__name":"china",
         "time":1996
      },
      {
         "count":"1",
         "gdp_growth__avg":3.79848988541973,
         "geo__name":"united states of america",
         "time":1996
      }
]
}

I would to Map and Reduce and generate a new object containing a summation of the GDP growth for all the countries in the above JSON that might look roughly like this:

{  
  {
     "gdp_growth__avg":46.23,
     "geo__name":"united states of america",
  },
  {
     "gdp_growth__avg":16.23,
     "geo__name":"china",
  },
  {
     "gdp_growth__avg":36.23,
     "geo__name":"russia",
  },
  {
     "gdp_growth__avg":26.23, 
     "geo__name":"botswana",
     "time":1991
  }
 }

I have looked at map and reduce and am not sure how best to proceed.

I was thinking something like this might be moving in the right directions, but does not seem to do what I was expecting:

      var arr = [{x:1},{x:2},{x:4}];

      arr.reduce(function (a, b) {
        return {x: a.x + b.x};
      });

      console.log(arr); //Outputs that same initial array

While I recognize that it is probably better and easier to do this on the server-side, I am wondering if what I am trying to do can be done on the client side with JavaScript. Any suggestions? Thanks in advance.

You want console.log(arr.reduce(…)). reduce does not alter the array (or even reassign the variable), it just returns a value. — Bergi
– Bergi, Commented Dec 1, 2015 at 0:05
@Bergi, +1 because i learned something here that i did not expect. Thank you. — MrEhawk82
– MrEhawk82, Commented Dec 1, 2015 at 0:32
map and reduce can be used server side too if you use node. Probably whatever your server can run can do it. Most convenient in js or python (are there python-based servers?) — sqykly
– sqykly, Commented Dec 1, 2015 at 1:12

Mr. Concolato · Accepted Answer · 2015-12-03 15:03:08Z

14

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 
   }

edited Dec 3, 2015 at 15:03

Mr. Concolato

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answered Dec 1, 2015 at 1:03

marsgpl

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Comments

Mike Baranczak · Accepted Answer · 2015-12-01 00:10:42Z

4

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

answered Dec 1, 2015 at 0:10

Mike Baranczak

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2 Comments

Bergi Over a year ago

No, it does not return a new array.

Shubham Dixit Over a year ago

it depends on the type of accumulator we use, it can be json object or even a js Map ,but array.map() returns a new array

Abhilash Patel · Accepted Answer · 2020-02-25 16:37:32Z

1

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
  }
]

answered Feb 25, 2020 at 16:37

Abhilash Patel

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Comments

Ravindra Gullapalli · Accepted Answer · 2022-04-04 18:39:11Z

1

You can try something like this:

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

data.cells.map(function(datum) {
  return {
    geo__name: datum.geo__name,
    gdp_growth__avg: data.cells.filter(function(o) {
      return o.geo__name === datum.geo__name;
    }).reduce(function(sum, o) {
      return sum + o.gdp_growth__avg;
    }, 0)
  };
})

Needless to say, you can extract other properties from datum as well, such as time. I haven't.

edited Apr 4, 2022 at 18:39

Ravindra Gullapalli

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answered Dec 1, 2015 at 0:15

Hunan Rostomyan

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Comments

Ravindra Gullapalli · Accepted Answer · 2022-04-04 18:45:03Z

1

To the solution given by @Hunan, I added https://stackoverflow.com/a/53294268/341117 to get result without duplicates

The final solution I used is :

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

data =  data.cells.map(function(datum) {
  return {
    geo__name: datum.geo__name,
    gdp_growth__avg: data.cells.filter(function(o) {
      return o.geo__name === datum.geo__name;
    }).reduce(function(sum, o) {
      return sum + o.gdp_growth__avg;
    }, 0)
  };
}).filter((obj, pos, arr) => {
        return arr.map(mapObj =>
              mapObj.geo__name).indexOf(obj.geo__name) == pos;
        });

JS Fiddle - https://jsfiddle.net/8b4z3yc5/

answered Apr 4, 2022 at 18:45

Ravindra Gullapalli

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