Big O in JS: The basic that you need to know, see more at: https://medium.com/p/a5abb45570fa

peopleData.js

const people = [
  {
    name: "Joseph",
    age: 32,
    gender: "male",
  },
  {
    name: "Anna",
    age: 27,
    gender: "female",
  },
  {
    name: "Patrick",
    age: 31,
    gender: "male",
  },
  {
    name: "Ricardo",
    age: 32,
    gender: "male",
  },
  {
    name: "Lisa",
    age: 27,
    gender: "male",
  },
];

const peopleData = () => {
  const total = people.length;
  const names = people.map(({ name }) => name);

  const peopleWithSameAge = people.filter(
    ({ age }) => people.filter(person => person.age == age).length > 1,
  );

  return {
    total,
    names,
    peopleWithSameAge,
  };
};



/* will output: 
{ total: 5,
  names: [ 'Joseph', 'Anna', 'Patrick', 'Ricardo', 'Lisa' ],
  peopleWithSameAge: 
   [ { name: 'Joseph', age: 32, gender: 'male' },
     { name: 'Anna', age: 27, gender: 'female' },
     { name: 'Ricardo', age: 32, gender: 'male' },
     { name: 'Lisa', age: 27, gender: 'male' } ] }

*/