Javascript: merge objects by key

Question

I have an array of objects that looks like this:

var countries = [
    {id: SWE, value: 5},
    {id: DE, value:10},
    {id: SWE, anotherValue: 11},
    {id: DE, anotherValue: 15}
]

I want to merge array elements by id. The result should look like this:

countries = [
    {id: SWE, value: 5, anotherValue: 11},
    {id: DE, value:10, anotherValue:15}
]

Right now, I'm doing this with a for loop and a lot of if and else.

Question: is there any (more elegant) javascript inbuilt functionality to achieve this?

I've tried googling this, the problem is that I'm not sure what to Google for (I'm a javascript newby). Any help is appreciated.

Do you mean an array of objects? countries is currently not a valid object, the objects within it do not have any keys. — Mark Walters
– Mark Walters, Commented Nov 16, 2015 at 8:45
Certainly there is no built in JavaScript functionality to do this. You would need a third party library — major-mann
– major-mann, Commented Nov 16, 2015 at 8:46
Also you have SW and SWE merging together to make SWE. Please fix your question and we'll take a look. — PeteB
– PeteB, Commented Nov 16, 2015 at 8:46
What happened to the one with ID "SW" ? Or was that supposed to be "SWE"? Please explain your functionality further so that we can help you. It looks like you are finding all the same ID's ( If id: "SW" was supposed to be "SWE" ), and keeping only the largest values? I see no way to do this with built in javascript in any case. you will have to make the code yourself. This isn't a generic enough case for it to be built in. — Sean_A91
– Sean_A91, Commented Nov 16, 2015 at 8:47
You can do this yourself. Just iterate through the array and combine this object. — Yeldar Kurmangaliyev
– Yeldar Kurmangaliyev, Commented Nov 16, 2015 at 8:50

MoLow · Accepted Answer · 2015-11-16 09:05:42Z

4

try this:

function mergeById(a){
  var obj={};
  
  a.forEach(function(e){
    if(e && e.id){
      obj[e.id] = obj[e.id] || {};    
      for(var _k in e) obj[e.id][_k] = e[_k]
    }
  });       
  
  return Object.keys(obj).map(function (key) {return obj[key]});
}

var countries = [
    {id: 'SWE', value: 5},
    {id: 'DE', value:10},
    {id: 'SWE', anotherValue: 11},
    {id: 'DE', anotherValue: 15}
]
document.write(JSON.stringify(mergeById(countries)))

edited Nov 16, 2015 at 9:05

answered Nov 16, 2015 at 8:55

MoLow

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1 Comment

seb Over a year ago

No if and else. that looks way more elegant than what I've got.

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