Javascript convert list of objects to map of maps

Question

I am new to Javascript. I am working on converting list of objects to map of maps using javascript.
Below is the code I have written.

 var person = { firstName: "John", lastName: "Doe", rank: 0, rollNo: "0201", school: "test", id: 0 }; var person1 = { firstName: "John1", lastName: "Doe1", rank: 0, rollNo: "0201", school: "test1", id: 1 }; var testList = [] var testList1 = [] var slotObject = {} var slotObjectMap = {}; var finalObject = {}; testList.push(person); testList.push(person1); console.log(testList); for (let i = 0; i < testList.length; i++) { slotObject["firstName"] = testList[i].firstName; slotObject["lastName"] = testList[i].lastName; slotObject["rollNo"] = testList[i].rollNo; slotObject["rank"] = testList[i].rank; slotObject["school"] = testList[i].school; testList1.push(slotObject); if (finalObject[testList[i]]) { console.log("yes"); slotObjectMap = {}; } else { slotObjectMap = finalObject[testList[i].school]; } slotObjectMap[testList[i].id] = slotObject; finalObject[testList[i].school] = slotObjectMap; } console.log(slotObjectMap); console.log(finalObject); // Display some data from the object: document.getElementById("demo").innerHTML = person.firstName;

 <h2>JavaScript Objects</h2> <p id="demo"></p>

My expected output is:

{ test:{
   0:{firstName: "John", lastName:"Doe", rank:0, rollNo:"0201", school:"test"}, 
   }, 
 test1:{
   1:{firstName: "John1", lastName:"Doe1", rank:0, rollNo:"0201", school:"test1"}
   }
}

My above code is not working as expected. Not sure where things are going wrong.
Please help.

My eventual goal is to covert above objects(person, person1) in to below output. Is this is possible using arrays reduce?

[ { additionalInfo : ''
  , school         : 'test'
  , randomValue    : ''
  , studentInfo: 
    [ { rank      : 0
      , rollNo    : '0201'
      , firstName : 'John'
      , lastName  : 'Doe'
  } ] } 
, { additionalInfo : ''
  , school         : 'test1'
  , randomValue    : ''
  , studentInfo: 
    [ { rank      : 0
      , rollNo    : '0201'
      , firstName : 'John1'
      , lastName  : 'Doe1'
  } ] } 
] 

Answer 1

Not 100% sure what all your code with slotObject etc is all about.

But looking at your expected output, it looks like you want to use reduce, with school as a key that you use to reduce into..

eg.

 var person = { firstName: "John", lastName: "Doe", rank: 0, rollNo: "0201", school: "test", id: 0 }; var person1 = { firstName: "John1", lastName: "Doe1", rank: 0, rollNo: "0201", school: "test1", id: 1 }; const r = [person, person1].reduce( (a, v) => { //extract school & id, const {school, id, ...other} = v; //lets make sure school exists a[school] = a[school] || {}; //lets add back school to other, and assign //and use id as another sub key into school. a[school][id] = {...other ,school}; return a}, {}); console.log(r);

 <h2>JavaScript Objects</h2> <p id="demo"></p>

Answer 2

You can't use Array.map because this method return an Array and you are expecting an Object.
just learn about array.reduce and Destructuring assignment

 var person = { firstName:"John", lastName:"Doe", rank:0, rollNo:"0201", school:"test", id:0 } , person1 = { firstName:"John1", lastName:"Doe1", rank:0, rollNo:"0201", school:"test1", id:1 } ; let testList = [ person, person1 ] let result = testList.reduce((r,{school, id, ...info})=> { r[school] = {} r[school][id] = {...info, school } return r } ,{}) console.log( result )

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for the question update
(and comments part from PO - on chat)

 let testList = [ { firstName:"John", lastName:"Doe", rank:0, rollNo:"0201", school:"test", id:1 } , { firstName:"John1", lastName:"Doe1", rank:0, rollNo:"0201", school:"test1", id:2 } , { firstName:"John2", lastName:"Doe2", rank:0, rollNo:"0202", school:"test1", id:3 } , { firstName:"John3", lastName:"Doe3", rank:0, rollNo:"0203", school:"test", id:5 } ] , result = testList.reduce((res,{ firstName, lastName, rank, rollNo, school })=> { let line = res.find(x=>x.school===school) if (!line) { line = { additionalInfo:'', school, randomValue:'', studentInfo:[] } res.push(line) } line.studentInfo.push({ rank, rollNo, firstName, lastName }) return res } ,[] ) console.log( result )

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