javascript - 如何使用reduce函数有效地评估javascript数组中的元素

Question

我有一个名为people 的数组，它是一个对象数组(人的 名字和他/她的城市 的名字)，以及我想制作一个函数来计算该数组中不同城市的总数。我使用了一个使用 for 循环的函数，但在 javascript 中使用 reduce 函数似乎是更好的方法。这是片段

const people = [
  { name: "Jessica", city: "New York"},
  { name: "Steve",   city: "Los Angels"},
  { name: "Peter",   city: "Boston"},
  { name: "Elaine",  city: "Montreal"},
  { name: "Chris",  city: "Montreal"},
  { name: "Mike",  city: "Boston"},
  { name: "George",  city: "Vancouver"},
];
let nbre_distinct_cities = 0;

countDistinctCity(people);
console.log('Total number of distinct cities: ',nbre_distinct_cities); 

function countDistinctCity(people)
{
  for(let i = 0; i < people.length; i++)
  {
      if(i === people.length - 1)
      {
          break;
      }
      else if(people[i].city !== people[i + 1].city)
      {
        nbre_distinct_cities++
      }
  }

}

如果有人建议使用 reduce() 函数的高效函数，我将不胜感激

Answer 1

您可以使用 Set存储数组中的所有城市，并且由于集合只有唯一条目，集合的最终大小将为您提供不同城市的数量:

const people = [
  { name: "Jessica", city: "New York"},
  { name: "Steve",   city: "Los Angels"},
  { name: "Peter",   city: "Boston"},
  { name: "Elaine",  city: "Montreal"},
  { name: "Chris",  city: "Montreal"},
  { name: "Mike",  city: "Boston"},
  { name: "George",  city: "Vancouver"},
];

let nbre_distinct_cities = new Set(people.map(({city}) => city)).size;
console.log('Total number of distinct cities: ', nbre_distinct_cities);