population

export default function (data) {
    let cities = [...data.cities];
    let people = [...data.people];

    const citiesWithPopulation = cities.reduce((city, elem) => {

        const id = elem.id;
        let obj = {name: elem.name, id: elem.id, citizens: [], population: 0};

        people.map((per) => {
            if(id === per.city) {
                obj.citizens.push(per.name);
            }
        });

        obj.population = obj.citizens.length;

        city.push(obj);

        return city;
    }, [])

    const peopeUpdated = people.reduce((arr, elem) => {

    let person = {name: elem.name, city: {}};

    citiesWithPopulation.map (el => {
        if (el.id === elem.city) {
            person.city = {name: el.name, population: el.population};
        }
        })

        arr.push(person);

        return arr;
    },[])

    return peopeUpdated;

}