Merge array of objects dynamically with same key

Question

I want to merge a single array of multiple objects dynamically with the same key. An example of the data is this:

var data = [{
  ReportTime: "30 Apr 2017BDT",
  Rate: "1.00000",
  AvgGrowth: "0.0"
}, {
  ReportTime: "30 Apr 2017BDT",
  Rate: "0.01107",
  AvgGrowth: "0.1"
}, {
  ReportTime: "29 Apr 2017BDT",
  Rate: "1.00000",
  AvgGrowth: "0.0"
}, {
  ReportTime: "29 Apr 2017BDT",
  Rate: "0.01107",
  AvgGrowth: "-0.5"
}]

I want to generate data like this

newData = [{
  "30 Apr 2017BDT",
  "1.00000",
  "0.0",
  "0.01107",
  "0.1"
}, {
  "29 Apr 2017BDT",
  "1.00000",
  "0.0",
  "0.01107",
  "-0.5"
}];

I need a suggestion or help how can I resolve this issue.

Key is `ReportTime` when we find the same Report time we need to merge that object — Parth Raval, Apr 08 '20 at 09:18
The data structure you're trying to create is invalid as the properties in the objects have no value. — Rory McCrossan, Apr 08 '20 at 09:19
@RoryMcCrossan Okay, can you please let me know how can I merge two objects with the same property name in a single array? — Parth Raval, Apr 08 '20 at 09:21
why is rate and avg growth not merged in your output? They are just new properties.. — raven, Apr 08 '20 at 09:22
@raven what I need to do is, I have to compare Report time and based on that have to merge two objects — Parth Raval, Apr 08 '20 at 09:25

score 1 · Answer 1 · answered Apr 08 '20 at 09:25

You can use reduce to group values by ReportTime

const data = [{ ReportTime: "30 Apr 2017BDT", Rate: "1.00000", AvgGrowth: "0.0"}, { ReportTime: "30 Apr 2017BDT", Rate: "0.01107", AvgGrowth: "0.1"}, { ReportTime: "29 Apr 2017BDT", Rate: "1.00000", AvgGrowth: "0.0"
}, { ReportTime: "29 Apr 2017BDT", Rate: "0.01107", AvgGrowth: "-0.5"}]

const merged = data.reduce((op, inp) => {
  let key = inp.ReportTime
  op[key] = op[key] || []
  op[key].push(inp)
  return op
}, Object.create(null))

console.log(merged)

Mohammad Usman · Accepted Answer · 2020-04-08T10:47:48.833

Your expected output doesn't looks a valid JS. You can however get an array of arrays by iterating over the array using a couple of methods like .reduce(), .map() and Object.entries():

const data = [
  {ReportTime: "30 Apr 2017BDT", Rate: "1.00000", AvgGrowth: "0.0"},
  {ReportTime: "30 Apr 2017BDT", Rate: "0.01107", AvgGrowth: "0.1"},
  {ReportTime: "29 Apr 2017BDT", Rate: "1.00000", AvgGrowth: "0.0"},
  {ReportTime: "29 Apr 2017BDT", Rate: "0.01107", AvgGrowth: "-0.5"}
];

const result = Object.entries(
  data.reduce((r, {ReportTime, ...rest}) => {
    r[ReportTime] = (r[ReportTime] || []).concat(Object.values(rest));
    return r;
  }, {})
).map(([k, v]) => [k, ...v]);

console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

Here is an alternate approach which uses es5(old) syntax:

var data = [
  {ReportTime: "30 Apr 2017BDT", Rate: "1.00000", AvgGrowth: "0.0"},
  {ReportTime: "30 Apr 2017BDT", Rate: "0.01107", AvgGrowth: "0.1"},
  {ReportTime: "29 Apr 2017BDT", Rate: "1.00000", AvgGrowth: "0.0"},
  {ReportTime: "29 Apr 2017BDT", Rate: "0.01107", AvgGrowth: "-0.5"}
];
var key = 'ReportTime';

var reducer = function(data, key) {
  var result = [];
  var map = {};
  
  data.forEach(function(o, i) {
    map[o[key]] = map[o[key]] || [];
    
    for(var k in o) {
      if(!(k === key)) { map[o[key]].push(o[k]); }
    };
  });
  
  for(var j in map) {
    result.push([].concat(j, map[j]));
  };
  
  return result;
};

console.log(reducer(data, key));

This is what exactly I want as the solution but gives me an error `Property 'values' does not exist on type 'ObjectConstructor'.` — Parth Raval, Apr 08 '20 at 09:40
@ParthRaval Are you using typescript? If yes then here is the answer.. https://stackoverflow.com/questions/52304422/property-values-does-not-exist-on-type-objectconstructor — Mohammad Usman, Apr 08 '20 at 09:41

score 1 · Answer 3 · answered Apr 08 '20 at 09:29

I think if make group ReportTime's into object with maintaining Rate and AvgGrowth will be helpful.

Go over items, Build an object with keys as "ReportTime". When ReportTime already exist in object, just update the Rate and AvgGrowth. After the iteration, Get Object.values() of above object to get it as array.

const update = data => {
  const res = {};
  data.forEach(item => {
    if (!res[item.ReportTime]) {
      res[item.ReportTime] = {
        ReportTime: item.ReportTime,
        Rate: [],
        AvgGrowth: []
      };
    }
    res[item.ReportTime].Rate.push(item.Rate);
    res[item.ReportTime].AvgGrowth.push(item.AvgGrowth);
  });
  return Object.values(res);
};

var data = [
  {
    ReportTime: "30 Apr 2017BDT",
    Rate: "1.00000",
    AvgGrowth: "0.0"
  },
  {
    ReportTime: "30 Apr 2017BDT",
    Rate: "0.01107",
    AvgGrowth: "0.1"
  },
  {
    ReportTime: "29 Apr 2017BDT",
    Rate: "1.00000",
    AvgGrowth: "0.0"
  },
  {
    ReportTime: "29 Apr 2017BDT",
    Rate: "0.01107",
    AvgGrowth: "-0.5"
  }
];

console.log(update(data));

Merge array of objects dynamically with same key

3 Answers3