How to change array object to nested object in javascript

Question

I would like to know how to change array object to nested object in javascript. I have list as array object, how to convert to nested object

function nestedobj(arrlist){
  var result ={};
  result.list1 = arrlist[0];
  result.list2 = arrlist[1]
  return list;
}


var list= [
  {id: 1, cn: "SG"},
  {id: 2, cn: "TH"}
]

var list1= [
  {id: 1, cn: "SG"},
  {id: 2, cn: "TH"},
  {id: 3, cn: "MY"}
]

var listobj = this.nestedobj(list);
var listobj1 = this.nestedobj(list1);

console.log(listobj)
console.log(listobj1)

Expected Output

{
  "list1":{"id": 1, "cn": "SG"},
  "list2":{"id": 2, "cn": "TH"}
}

{
  "list1":{"id": 1, "cn": "SG"},
  "list2":{"id": 2, "cn": "TH"},
  "list3":{"id": 3, "cn": "MY"}
}

I made a snippet - moving the call to AFTER the objects stopped the error — mplungjan
– mplungjan, Commented Apr 3, 2020 at 9:05
You pass list to nestedobj() before you define it, so it's undefined — Chayim Friedman
– Chayim Friedman, Commented Apr 3, 2020 at 9:05
@ChayimFriedman that is just one issue - the output is not according to spec — mplungjan
– mplungjan, Commented Apr 3, 2020 at 9:06

Pranav C Balan · Accepted Answer · 2020-04-03 09:17:01Z

5

You can use Array#reduce method(or simple loop) to generate the object where id property or index can be used to generate the property name.

var list = [{id: 1,    cn: "SG"  },  {    id: 2,    cn: "TH"  }]

var list1 = [{    id: 1,    cn: "SG"  },  {    id: 2,    cn: "TH"  },  {    id: 3,    cn: "MY"  }]

function convert(arr) {
  // iterate over the array
  return arr.reduce((obj, o, i) => {
    // define the property
    obj[`list${o.id}`] = o; 
    // or with index obj[`list${i + 1}`] = o;
    // return object reference for next call
    return obj;
    // set initial value as empty object to keep the result
  }, {})
}

// or with simple loop
function convert1(arr) {
  const result = {};
  for (let o of arr)
    result[`list${o.id}`] = o;
  return result
}

console.log(convert(list));
console.log(convert(list1));

console.log(convert1(list));
console.log(convert1(list1));

edited Apr 3, 2020 at 9:17

answered Apr 3, 2020 at 9:05

Pranav C Balan

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2 Comments

Sen Over a year ago

@Pranav C Balan, thanks for reply, how to convert the result nested object to array i.e get the output as input , tried let convertobj = Object.keys(listoutput).map(function(k) { return listouput[k] })

Pranav C Balan Over a year ago

@miyavv : Object.values(listoutput) is also fine

xdeepakv · Accepted Answer · 2020-04-03 09:17:46Z

// Loop an collect:

var list = [
      { id: 1, cn: "SG" },
      { id: 2, cn: "TH" }
    ];
    
    var list1 = [
      { id: 1, cn: "SG" },
      { id: 2, cn: "TH" },
      { id: 3, cn: "MY" }
    ];
    
    function nestedobj2(list) {
      let result = {};
      for (const v of list) {
        result["list" + v.id] = v;
       }
     return result;
    }

var listobj = nestedobj2(list);
console.log("%j", listobj);
listobj = nestedobj2(list1);
console.log("%j", listobj);
   
   function nestedobj(list) {
      return list.reduce((x, data) => {
        x["list" + data.id] = data;
        return x;
      }, {});
    }
    
     listobj = nestedobj(list);
    console.log("%j", listobj)
    listobj = nestedobj(list1);
    console.log("%j", listobj)

.as-console-row {color: blue!important}

Jaromanda X · Accepted Answer · 2020-04-03 09:27:06Z

If the number after list is the ordinal position of the item plus one

var nestedobj = a => Object.fromEntries(Object.entries(a).map(([k, v]) => [`list${+k+1}`, v]));

var list= [
  {id: 1, cn: "SG"},
  {id: 2, cn: "TH"}
]

var list1= [
  {id: 1, cn: "SG"},
  {id: 2, cn: "TH"},
  {id: 3, cn: "MY"}
]

var listobj = nestedobj(list);
var listobj1 = nestedobj(list1);
console.log(listobj)
console.log(listobj1)

If however, the number after list relates to the id of the object

var nestedobj = a => Object.fromEntries(Object.values(a).map(v => [`list${v.id}`, v]));

var list= [
  {id: 1, cn: "SG"},
  {id: 2, cn: "TH"}
]

var list1= [
  {id: 1, cn: "SG"},
  {id: 2, cn: "TH"},
  {id: 3, cn: "MY"}
]

var listobj = nestedobj(list);
var listobj1 = nestedobj(list1);
console.log(listobj)
console.log(listobj1)

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