JavaScript arrays new arrays based on elements

Question

I have an array as follows:

var data = [
  {code: '1', name: 'aa'},
  {code: '20', name: 'bb'},
  {code: '30', name: 'cc'},
  {code: '123', name: 'dd'}
]

I expect the new array to look like this:

 var newData = [
  {status: '1', code: '1', name: 'aa'},
  {status: '2', list: [
    {code: '20', name: 'bb'},
    {code: '30', name: 'cc'}
  ]},
  {status: '3', code: '123', name: 'dd'}
]
console.log(newData)

I tried to use a for loop, but the code is quite repetitive:

var temp = []
var list = []
for(var item in data){
 if (data[item].code === '1') {
  temp.push({
    status: '1',
    code: data[item].code,
    name: data[item].name
  })
 }
 if (data[item].code === '20' || data[item].code === '30') {
  list.push(data[item])
  temp.push({
    status: '2',
    list: list
  })
 }
 if (data[item].code === '123') {
  temp.push({
    status: '3',
    code: data[item].code,
    name: data[item].name
  })
 }
}

Where does the status property come from? Are you really supposed to hard-code it for 1, 20 / 30, and 123? — CertainPerformance
– CertainPerformance, Commented Nov 6, 2019 at 3:07
You have a list variable which is not get cleared after iteration. That will be already carrying data for previous iteration in for loop. — XPD
– XPD, Commented Nov 6, 2019 at 3:27

CertainPerformance · Accepted Answer · 2019-11-06 03:20:56Z

4

First create a mapping of each code to its associated status. Then iterate over the data, inserting into a new object indexed by status. If something at that status doesn't exist in the new object yet, create an object with a code property - otherwise, if it exists with a code property, turn it into an array, and push to that array.

At the end, take the values of the new object to turn it into the desired array format:

const statusByCode = {
  1: 1,
  20: 2,
  30: 2,
  123: 3,
}

var data = [
  {code: '1', name: 'aa'},
  {code: '20', name: 'bb'},
  {code: '30', name: 'cc'},
  {code: '123', name: 'dd'}
];
const dataByStatus = {};
for (const { code, name } of data) {
  const status = statusByCode[code];
  if (!dataByStatus[status]) {
    dataByStatus[status] = { status, code, name };
  } else {
    if (dataByStatus[status].code) {
      const { status: _, ...oldObj } = dataByStatus[status];
      dataByStatus[status] = { status, list: [oldObj] };
    }
    dataByStatus[status].list.push({ code, name });
  }
}

const output = Object.values(dataByStatus);
console.log(output);

answered Nov 6, 2019 at 3:20

CertainPerformance

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1 Comment

1053654645 Over a year ago

I understand! Thank you for your help!

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