Add array values into map using javascript?

Question

I have an array value as a with key:value pair. I wanted to map the same key array values as below format:

Expected Output: [abc: 1],[def:2,42,40]

Please find my code below:

var a = {"abc": 1, "def": 2, "def": 42, "def" : 40};    
var array_keys = new Array();
var array_values = new Array();
for (var key in a) {
    array_keys.push(key);
    array_values.push(a[key]);
}
alert(array_keys);
alert(array_values);

It returns the values as

My output : [abc:def] [1,40]

Any help on this?

You are currently just putting all keys in an array and all values in another -- the Output is actually [abc,def] [1,40]. — user887675
– user887675, Commented Jun 24, 2014 at 11:16
Its because JS expects every key in the array to be unique. This wouldnt work out of the box. If you change def's to 3 different keys, it works perfectly. — paradox
– paradox, Commented Jun 24, 2014 at 11:18
var a = {"abc": 1, "def": 2, "def": 42, "def" : 40}; actually produces Object {abc: 1, def: 40}. How are you actually getting your array values initially? — JamesA
– JamesA, Commented Jun 24, 2014 at 11:20
@Maniram, can't you change the structure to this: {"abc": [1], "def": [2, 42, 40]} ? — user2575725
– user2575725, Commented Jun 24, 2014 at 11:26

Andy · Accepted Answer · 2018-10-04 15:28:22Z

6

You can achieve something like what you want if you play around with your initial data structure:

Have an array of objects:

var a = [{abc: 1}, {def: 2}, {def: 42}, {def: 40}];

Set up a new object

var o = {};

And then loop over the data. For each object: if the key doesn't exist in o, the output object, add it and set its value to an array, otherwise just push the value of the object to the array.

for (var i = 0, l = a.length; i < l; i++) {
  var key = Object.keys(a[i]);
  if (!o[key]) { o[key] = []; }
  o[key].push(a[i][key]);
}

And you end up with an object the values of which are arrays:

console.log(o); // {abc: [1], def: [2,42,40] }

Demo

edited Oct 4, 2018 at 15:28

answered Jun 24, 2014 at 11:31

Andy

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2 Comments

Aj Otto Over a year ago

Hmmm, I wish this answer was updated with the new Javascript Map

Andy Over a year ago

You could write your own answer @AjOtto that does use Map.

Michael Kunst · Accepted Answer · 2014-06-24 11:21:03Z

2

var a = {"abc": 1, "def": 2, "def": 42, "def" : 40};

This is not possible. Object keys must be unique in javascript, so you can't add 3 different items with the same key ("def"). If you define multiple elements with the same key, at least chrome will take the last added value.

So answering your question: With the input provided there is no way to get you Expected output.

answered Jun 24, 2014 at 11:21

Michael Kunst

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