creating new object with values of another object in javascript

Question

How can we change the structure of the below data object using JavaScript. Needs to categorize all the names under the std. Thanks in advance

[
 {
 "name": "Rohan",
 "std": "3"
 },
 {
 "name": "Jack",
 "std": "2"
 },
 {
 "name": "Peter",
 "std": "2"
 }
]

to

[
 {
 "std": "2",
 "details": [
 {
 "name": "Jack"
 },
 {
 "name": "Peter"
 }
 ]
 },
 {
 "std": "3",
 "details": [
 {
 "name": "Rohan"
 }
 ]
 }
]

• Meet: Refer following link, i think this should help you:- stackoverflow.com/questions/15279685/restructure-json

Answer 1

The solution using Array.forEach, Array.map and Object.keys functions:

var arr = [{"name": "Rohan", "std": "3"}, { "name": "Jack", "std": "2" }, { "name": "Peter", "std": "2" }],
 grouped = {}, result;
arr.forEach(function(obj){
 var std = obj['std'];
 if (this[std]) {
 this[std]['details'].push({'name' : obj['name']});
 } else {
 this[std] = {'std' : std, 'details' : [{'name' : obj['name']}]};
 }
}, grouped);
result = Object.keys(grouped).map((k) => grouped[k]);
console.log(JSON.stringify(result, 0, 4));

The output:

[
 {
 "std": "2",
 "details": [
 {
 "name": "Jack"
 },
 {
 "name": "Peter"
 }
 ]
 },
 {
 "std": "3",
 "details": [
 {
 "name": "Rohan"
 }
 ]
 }
]

Answer 2

You can use reduce() method here

var data = [{
 "name": "Rohan",
 "std": "3"
 }, {
 "name": "Jack",
 "std": "2"
 }, {
 "name": "Peter",
 "std": "2"
 }],
 res = [],
 kmap = {};
res = data.reduce(function(a, b) {
 // check std value already in array using kmap object
 if (kmap[b.std]) {
 // if already exist then push name attribute in the details 
 a[kmap[b.std] - 1].details.push({
 'name': b.name
 });
 } else {
 // in else case push the new object 
 a.push({
 'std': b.std,
 'details': [{
 'name': b.name
 }]
 });
 kmap[b.std] = a.length; // storing the (index + 1) value to avoid 0 in if condition
 }
 return a;
}, []);
console.log(res);

For older browsers check polyfill option for reduce method.

Answer 3

Problems like this are good candidates for recursion. Here is one possible recursive solution. You can make it much prettier using a functional programming framework such as underscore.js.

var objs = [
{
 "name": "Rohan",
 "std": "3"
},
{
 "name": "Jack",
 "std": "2"
},
{
 "name": "Peter",
 "std": "2"
}
];
function categorize(objs) {
 if (objs.length === 0) {
 return [];
 } else {
 var first = objs.shift();
 var categorized = categorize(objs);
 for(var i = 0; i < categorized.length; i++) {
 if (categorized[i].std === first.std) {
 categorized[i].details.push({name: first.name});
 break;
 }
 }
 if(i === categorized.length) {
 categorized.push({std: first.std, details: [{name: first.name}]});
 }
 return categorized;
 }
}
var res = categorize(objs);
console.log(res);

Answer 4

If you're using lodash (I know the question didn't ask this and it's going to be slower, but it may be useful to someone :))

var data = [
 { "name": "Rohan", "std": "3" },
 { "name": "Jack", "std": "2" },
 { "name": "Peter", "std": "2" }
];
var grouped = _.chain(data)
 .groupBy('std')
 .map(function (people, std) {
 return {
 std: std,
 details: _.map(people, function(person) {
 return { name: person.name };
 })
 }
 }).value();