js object property creation from keys

Question

hi I am trying to create a object map from array of objects using reduce method but did n't find a way to add 2 properties as key . Let say I have array of objects like -

 const students = [
    {
      name: "sam",
      age: 26,
    },
    {
      name: "john",
      age: 30,
    }
    ]

i am trying to create a map like

{
  sam_26:{
      name: "sam",
      age: 26,
    }
 }

my code for reduce function :

students.reduce((obj, student) => {
    `${obj[student.name]}_${obj[student.age]}` = student;
    return obj;
  }, {});

this didn't work . any pointers will be helpful ..thanks!

Answer 1

Create the key with the values taken from the student object. Assign the current student to the obj (the accumulator) using the key:

const students = [{
    name: "sam",
    age: 26,
  },
  {
    name: "john",
    age: 30,
  }
];

const result = students.reduce((obj, student) => {
  const key = `${student.name}_${student.age}`;
  obj[key] = student;
  return obj;
}, {});

console.log(result);

A generic approach that uses a callback to create the key:

const keyBy = (arr, cb) => 
  arr.reduce((r, o) => {
    const key = cb(o);
    r[key] = o;
    return r;
  }, {});
  
const students = [{"name":"sam","age":26},{"name":"john","age":30}];  

const result = keyBy(students, (o) => `${o.name}_${o.age}`);

console.log(result);