Lets say I receive a parsed json like below:

[{"a":1},{"a":2},{"a":3}]

The keys are the same which is a.

How do I make each a unique so that the map is usable?'

EDIT1:

Results I want:

let myMap = {}; //I declare my variable
//Then I fetch a json and parse it
fetch(link)
    .then(function(response) {
      return response.json(); //parse the json string
    }).then(function(json) {
      myMap = json; //set it to myMap to be used
}

For some reason I having duplicate keys although you guys said the json is unique. Do I have to set the json string to myMap first and then only parse it?

Lets say I receive a parsed json like below:

[{"a":1},{"a":2},{"a":3}]

The keys are the same which is a.

How do I make each a unique so that the map is usable?'

EDIT1:

Results I want:

let myMap = {}; //I declare my variable
//Then I fetch a json and parse it
fetch(link)
    .then(function(response) {
      return response.json(); //parse the json string
    }).then(function(json) {
      myMap = json; //set it to myMap to be used
}

For some reason I having duplicate keys although you guys said the json is unique. Do I have to set the json string to myMap first and then only parse it?

• javascript
• json
• object
• dictionary
• ecmascript-6

• How should your output look like ? – Rayon Commented Jul 4, 2016 at 5:59
• Something like this {{ id: 1, flight_location: "KUL", description: "Kuala Lumpur" }, { id: 2, flight_location: "KIX", description: "Osaka-Kansai" }} – Joshua Rajandiran Commented Jul 4, 2016 at 6:00
• your a is already unique because u have unique values inside 1 , 2 , 3 like that or else create an object id and use dynamic unique id for each objects – Gayathri Mohan Commented Jul 4, 2016 at 6:01
• You could keep an index, append it to your "a" and increase it after each use. Alternatively, you could use a random number - depends on how long your json is expected to be since you need to keep in mind the same random number could be generated. – Sotiris Kiritsis Commented Jul 4, 2016 at 6:01
• BTW, you mean [ { a : 1 }, { a : 2 } .. ] or { { a : 1 }, { a : 2 } ..} ?? – Yourim Yi Commented Jul 4, 2016 at 6:03

5 Answers 5

Basically you can use an Object as hash table

var data = [{ "a": 1 }, { "a": 2 }, { "a": 3 }],
    object = Object.create(null);

data.forEach(function (el) {
    object[el.a] = el;
});

console.log(object);

Or a Map

var data = [{ "a": 1 }, { "a": 2 }, { "a": 3 }],
    map = new Map;

data.forEach(function (el) {
    map.set(el.a, el);
});

console.log(map.get(1));

The advantage of Map over an Object is, the key can be anything. The key is not converted to string. Maps can have an object or other primitive or not primitive values as key.

Also if you have a single value list or want to make sure it IS unique you can use the index supplied like this:

obj.map((item, index) => 
   ...
)}

Maybe this?

[{a:1},{a:2},{a:3}].map(function(item, index) { item.id = index; return item; });

Map in javascript doesnot need a unique id, it will iterate through all the value. so it will iterate through all the objects irrespective the fact that the key is same

eg:

var kvArray = [{key:1, value:10}, {key:2, value:20}, {key:3, value: 30}]
var reformattedArray = kvArray.map(function(obj){ 
var rObj = {};
  rObj[obj.key] = obj.value;
   return rObj;
});

Well, [{a:1},{a:2},{a:3}] is already unique... but, It's an Array. so you cannot access an object {a:2, ...} directly but find index with looping.

If I understand your question right way... you want to make new MAP with unique key a how about this way? - reduce can help us. :)

btw, Nina Scholz's answer is right.

let myMap = {}; //I declare my variable
//Then I fetch a json and parse it
fetch(link)
    .then(function(response) {
      return response.json(); //parse the json string
    }).then(function(json) {
      // myMap = json; //set it to myMap to be used

      myMap = json.reduce(function(p, n) { p[n.a] = n; return p; }, {});
      // n.a or n['a'] - primary key (in sample, [1,2,3...])
      // "myMap[1].foo", "myMap[2].bar"

      // or change KEY as your taste.
      myMap = json.reduce(function(p, n) { p['k' + n.a] = n; return p; }, {});
      // "myMap.k1.foo", "myMap.k2.bar"

      // It's unique but if you want everything...
      myMap = json.reduce(function(p, n) {
        var k = 'k' + n.a;
        if(p[k] !== undefined) { p[k] = n; }
        else if(Array.isArray(p[k])) { p[k].push(n); }
        else { p[k] = [p[k]] ; }
        return p;
      }, {});
}