How to add a lable to an object value in javascript

February 11, 2022

I have an array of objects that is grouped by index and would like to restructure and add labels to the response.

This is my original array:

let cars = [{'make': 'audi', 'model': 'RS3', 'transmition': 'automatic'}, {'make': 'audi', 'model': 'RS7', 'transmition': 'dual-clutch'}, {'make': 'bmw', 'model': '325is', 'transmition': 'manual'}, {'make': 'bmw', 'model': 'M2', 'transmition': 'dual-clutch'}]

Here is the source code used to group the array by make:

var groupedByMake = _.groupBy(
          cars,
          "make"
        );

The response looks like this:

{
  'audi':[{'model': 'RS3', 'transmition': 'automatic'}, {'model': 'RS7', 'transmition': 'dual-clutch'}],
  'bmw':[{'model': '325is', 'transmition': 'manual'}, {'model': 'M2', 'transmition': 'dual-clutch'}]
}

My desired outcome should look like this:

[{
  'make': 'audi',
   'types': [{'model': 'RS3', 'transmition': 'automatic'}, {'model': 'RS7', 'transmition': 'dual-clutch'}]
  },{
  'make': 'bmw',
  'types': [{'model': '325is', 'transmition': 'manual'}, {'model': 'M2', 'transmition': 'dual-clutch'}]
}]

Is this possible to achieve using JavaScript? If so can I get assistance to achieve this task.

>Solution :

You can use array.reduce to turn one array into another one and control whether you return a new element or accumulate values in existing one (prev):

let cars = [{'make': 'audi', 'model': 'RS3', 'transmition': 'automatic'}, {'make': 'audi', 'model': 'RS7', 'transmition': 'dual-clutch'}, {'make': 'bmw', 'model': '325is', 'transmition': 'manual'}, {'make': 'bmw', 'model': 'M2', 'transmition': 'dual-clutch'}];

let output = cars.reduce((acc, cur) => {
    let {make, ...obj} = cur;    
    let prev = acc.find(x => x.make === make);
    if(!prev) {
      acc.push({make,types:[obj]})
    } else {
      prev.types.push(obj);
    }
    return acc;
}, []);

console.log(output);