How to transform JavaScript hashmap?

Question

i'm trying to create a <String, Array()> map from a json object. Imagine i got this json structure:

[
    {
        "userId": "123123",
        "password": "fafafa",
        "age": "21"
    },
    {
        "userId": "321321",
        "password": "nana123",
        "age": "34"
    }
]

The map i want to create would be:

key (string), value (array)

{
    "userId": [
        "123123",
        "321321"
    ],
    "password": [
        "fafafa",
        "nana123"
    ],
    "age": [
        "21",
        "34"
    ]
}

Is it possible to do this? :/

Thanks in advance.

There is no such thing as a "json object" and I don't see what can be the object you display. Is that a string you receive ? — Denys Séguret
– Denys Séguret, Commented Feb 19, 2013 at 16:58
Best to explain what you want to do with that map, because it may be that you can just use the object. — Popnoodles
– Popnoodles, Commented Feb 19, 2013 at 16:58
@dystroy OP had used characters that were not being displayed because they had not indented the code. Did you not compare the two versions before commenting? — Popnoodles
– Popnoodles, Commented Feb 19, 2013 at 17:01

MrCode · Accepted Answer · 2013-02-19 17:53:18Z

8

Demo

var json = '[{"userId" : "123123", "password": "fafafa", "age": "21"}, {"userId" : "321321", "password" : "nana123", "age" : "34"}]';

var list = JSON.parse(json);
var output = {};

for(var i=0; i<list.length; i++)
{
    for(var key in list[i])
    {
        if(list[i].hasOwnProperty(key))
        {
            if(typeof output[key] == 'undefined')
            {
                output[key] = [];
            }
            output[key].push(list[i][key]);
        }
    }
}

document.write(JSON.stringify(output));

Outputs:

{"userId":["123123","321321"],"password":["fafafa","nana123"],"age":["21","34"]}

edited Feb 19, 2013 at 17:53

answered Feb 19, 2013 at 17:02

MrCode

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2 Comments

msqar Over a year ago

you are a genius! that's what i needed. Thanks! The thing is, how do i create the map dinamically to String, Array() if i don't know all the keys names?

MrCode Over a year ago

@user59574 I've edited it to work without having to define the keys.

maerics · Accepted Answer · 2013-02-19 17:44:06Z

3

function mergeAttributes(arr) {
  return arr.reduce(function(memo, obj) { // For each object in the input array.
    Object.keys(obj).forEach(function(key) { // For each key in the object.
      if (!(key in memo)) { memo[key] = []; } // Create an array the first time.
      memo[key].push(obj[key]); // Add this property to the reduced object.
    });
    return memo;
  }, {});
}

var json = '[{"userId" : "123123", "password": "fafafa", "age": "21"}, {"userId" : "321321", "password" : "nana123", "age" : "34"}]';

mergeAttributes(JSON.parse(json));
// {
//   "userId": ["123123", "321321"],
//   "password": ["fafafa", "nana123"],
//   "age": ["21", "34"]
// }

edited Feb 19, 2013 at 17:44

answered Feb 19, 2013 at 17:03

maerics

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5 Comments

maerics Over a year ago

@user59574: see the following ECMAScript 5th Edition functions - Array.reduce, Object.keys, and Array.forEach.

MrCode Over a year ago

Nice example usage of ECMAScript 5 but beware this won't work on anything older than Internet Explorer 9.

maerics Over a year ago

@MrCode: yes, quite true. IE<9 does not support these standard JavaScript functions that were added in a specification that was published in late 2009.

MrCode Over a year ago

@maerics which is a shame because there are some nice modern features in that spec.

msqar Over a year ago

@maerics hey, now is showing "arr.reduce is not a function" what's happening? (Firefox and Chrome ) :(

Binita Bharati · Accepted Answer · 2013-09-27 04:00:23Z

1

Javascript's JSON.stringify will help you to convert any JSON compliant object model into a JSON string.

answered Sep 27, 2013 at 4:00

Binita Bharati

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