How to add duplicate key elements in JavaScript Object?

Question

I want to make the following newArray using by following testArray.

newArray↓

    let newArray = [
        {section:"business",name:["Bob","John"]},
        {section:"H&R",name:["Jen","Bobby"]},
    ]

testArray↓

let test = [
    {section:"business",name:"Bob"},
    {section:"business",name:"John"},
    {section:"H&R",name:"Jen"},
    {section:"H&R",name:"Bobby"},
]

First of all, I tried to find some key elements using by filter method like below.

let newArray = test.filter((x:any,i,self)=>
                  self.indexOf(x.section)===i
             )

but this code output is []. So, how do I make code to get my expected output? Does anyone help me?

question from:https://stackoverflow.com/questions/65878412/how-to-add-duplicate-key-elements-in-javascript-object

Answer 1

Use Array.reduce():

let test=[{section:"business",name:"Bob"},{section:"business",name:"John"},{section:"H&R",name:"Jen"},{section:"H&R",name:"Bobby"}];

let newArray = test.reduce((acc,cur) => {
  if(acc.some(el => el.section === cur.section)){
    acc.forEach((el,idx) => {
      if(el.section === cur.section){
        acc[idx].name.push(cur.name)
      }
    })
  }else{
    cur.name = [cur.name]
    acc.push(cur)
  }
  return acc
},[])

console.log(newArray)