Creating object array from key-value pairs

Question

From a service I receive a JSON object with key-value pairs, and I need to dynamically create objects from them, grouped by one column.

The JSON looks like this:

[
    { "Group" : "A", "Key" : "Name", "Value" : "John" },
    { "Group" : "A", "Key" : "Age",  "Value" : "30" },
    { "Group" : "A", "Key" : "City", "Value" : "London" },
    { "Group" : "B", "Key" : "Name", "Value" : "Hans" },
    { "Group" : "B", "Key" : "Age",  "Value" : "35" },
    { "Group" : "B", "Key" : "City", "Value" : "Berlin" },
    { "Group" : "C", "Key" : "Name", "Value" : "José" },
    { "Group" : "C", "Key" : "Age",  "Value" : "25" },
    { "Group" : "C", "Key" : "City", "Value" : "Madrid" }
]

I would need to transform it to the following array of objects:

[
    { Group : "A", Name : "John", Age : 30, City : "London" },
    { Group : "B", Name : "Hans", Age : 35, City : "Berlin" },
    { Group : "C", Name : "José", Age : 25, City : "Madrid" }
]

Each group can contain any number of key-value pairs.

Currently I have a working solution for this, but I don't know if it's optimal:

var items = [
    { "Group" : "A", "Key" : "Name", "Value" : "John" },
    { "Group" : "A", "Key" : "Age",  "Value" : "30" },
    { "Group" : "A", "Key" : "City", "Value" : "London" },
    { "Group" : "B", "Key" : "Name", "Value" : "Hans" },
    { "Group" : "B", "Key" : "Age",  "Value" : "35" },
    { "Group" : "B", "Key" : "City", "Value" : "Berlin" },
    { "Group" : "C", "Key" : "Name", "Value" : "José" },
    { "Group" : "C", "Key" : "Age",  "Value" : "25" },
    { "Group" : "C", "Key" : "City", "Value" : "Madrid" }
], item, record, hash = {}, results = [];

// Create a "hash" object to build up
for (var i = 0, len = items.length; i < len; i += 1) {
    item = items[i];

  if (!hash[item.Group]) {
    hash[item.Group] = {
      Group : item.Group
    };
  }
  hash[item.Group][item.Key] = item.Value;
}

// Push each item in the hash to the array
for (record in hash) {
  if(hash.hasOwnProperty(record)) {
    results.push(hash[record]);
  }
}

You can check the fiddle here: http://jsbin.com/ozizom/1/

Do you have a better solution for this?

Answer 1

Assuming that the JSON records will always be sorted by Group, here is another approach:

var json = [
    { "Group" : "A", "Key" : "Name", "Value" : "John" },
    { "Group" : "A", "Key" : "Age",  "Value" : "30" },
    { "Group" : "A", "Key" : "City", "Value" : "London" },
    { "Group" : "B", "Key" : "Name", "Value" : "Hans" },
    { "Group" : "B", "Key" : "Age",  "Value" : "35" },
    { "Group" : "B", "Key" : "City", "Value" : "Berlin" },
    { "Group" : "C", "Key" : "Name", "Value" : "José" },
    { "Group" : "C", "Key" : "Age",  "Value" : "25" },
    { "Group" : "C", "Key" : "City", "Value" : "Madrid" }
];

var array = [];
var previousGroup = null;

for(var i=0; i<json.length; i++) {
    var group = json[i].Group;
    if(previousGroup != group) {
        array.push({Group: group});
        previousGroup = group;
    }
    array[array.length-1][json[i].Key] = json[i].Value;
}

Here is a working example.

Answer 2

Here's a solution where the code size is reduced (for better or for worse :-) by the use of JavaScript idioms. This solution doesn't depend on the order of input values:

var values = [
  {Group: 'A', Key: 'Name', Value: 'John'},
  {Group: 'A', Key: 'Age', Value: '30'},
  {Group: 'A', Key: 'City', Value: 'London'},
  {Group: 'B', Key: 'Name', Value: 'Hans'},
  {Group: 'B', Key: 'Age', Value: '35'},
  {Group: 'B', Key: 'City', Value: 'Berlin'},
  {Group: 'C', Key: 'Name', Value: 'José'},
  {Group: 'C', Key: 'Age', Value: '25'},
  {Group: 'C', Key: 'City', Value: 'Madrid'}
];

var map = {};
values.forEach(function(value) {
  map[value.Group] = map[value.Group] || {Group: value.Group};
  map[value.Group][value.Key] = value.Value;
});

var results = Object.keys(map).map(function(key) { return map[key]; });

A working example is at http://jsfiddle.net/arQww .

Here's the fastest solution I can find, which assumes that the values will always be sorted by Group:

var group, results = [];
for (var i = 0; i < values.length; ) {
  results.push({Group: group = values[i].Group});
  do {
    results.push[results.length - 1][values[i].Key] = values[i].Value;  
  } while (++i < values.length && values[i].Group == group);
}

A performance comparison is at http://jsperf.com/vnmzc . While this second solutions is faster, the performance of both is O(n) and the real-world difference between them will be inconsequential, so the first solution is probably preferable since it's simpler and more general.

Answer 3

If you have to manipulate data a lot I would recommend underscore framework. This is how solution will look in it:

/*
 We group items into object that looks like {group: attributes, ..}
 Then for each group we create result object denoting group,
 and extend result with object created from keys and values of attributes
*/
_.map(_.groupBy(items, function (item) {return item.Group}),
     function (attributes, group) {
        return _.extend({Group: group},
                        _.object(_.pluck(attributes, 'Key'),
                                 _.pluck(attributes, 'Value')))
    })

Answer 4

I need help with a similar problem, buy I want to sum values. I have this array with objects

var myArrWithObj = [
    {DateToSort: "Jul2014", ValueOneToSum: "60", ValueTwoToSum: "15"},
    {DateToSort: "Jul2014", ValueOneToSum: "30", ValueTwoToSum: "50"},
    {DateToSort: "Jul2014", ValueOneToSum: "12", ValueTwoToSum: "22"},
    {DateToSort: "Aug2014", ValueOneToSum: "65", ValueTwoToSum: "25"},
    {DateToSort: "Aug2014", ValueOneToSum: "13", ValueTwoToSum: "10"},
    {DateToSort: "Aug2014", ValueOneToSum: "90", ValueTwoToSum: "20"},
    {DateToSort: "Sep2014", ValueOneToSum: "60", ValueTwoToSum: "15"},
    {DateToSort: "Sep2014", ValueOneToSum: "60", ValueTwoToSum: "18"},
    {DateToSort: "Sep2014", ValueOneToSum: "75", ValueTwoToSum: "18"}
                   ];

and I want the user to choose what month to sum from an option menu.

So If the user selects August 2014 from the select menu, I want to sum all the ValueOneToSum values and ValueTwoToSum values based on Aug2014 , how could I do that?

For example: the totalSumOne for Aug2014 would be 168 and totalSumTwo would be 55 .