如何获取对象数组中的值？答案

【问题标题】：How to get values in an array of objects?如何获取对象数组中的值？
【发布时间】：2020-04-20 11:31:36
【问题描述】：

我想从下面的数组中收集所有评分高于 3 的电影 id

let movies = [
  {'name': 'Actions', 'movies': [{'id': 1, 'rating': 2}, 
                                 {'id': 2, 'rating': 1}, 
                                 {'id': 3, 'rating': 4}]},
  {'name': 'Comedy', 'movies': [{'id': 4, 'rating': 3}, 
                                 {'id': 5, 'rating': 4}, 
                                 {'id': 6, 'rating': 5}]},
  {'name': 'Sci-fi', 'movies': [{'id': 7, 'rating': 1}, 
                                 {'id': 8, 'rating': 5}, 
                                 {'id': 9, 'rating': 2}]}
];

我从下面的代码中得到了评分高于 3 的 id

let res = movies
          .map( m => m.movies
                    .filter( f => f.rating > 3 ) 
          )
          .flat();
console.log(res);

输出

[[object Object] {
  id: 3,
  rating: 4
}, [object Object] {
  id: 5,
  rating: 4
}, [object Object] {
  id: 6,
  rating: 5
}, [object Object] {
  id: 8,
  rating: 5
}]

我怎样才能从我的输出中去掉 [object Object] 和 rating 并只得到扁平的 id 数组？

【问题讨论】：

标签： javascript angular multidimensional-array

【解决方案1】：

使用Array.flatMap()将电影展平为一个数组，通过rating进行过滤，然后映射到ids：

const movies = [{"name":"Actions","movies":[{"id":1,"rating":2},{"id":2,"rating":1},{"id":3,"rating":4}]},{"name":"Comedy","movies":[{"id":4,"rating":3},{"id":5,"rating":4},{"id":6,"rating":5}]},{"name":"Sci-fi","movies":[{"id":7,"rating":1},{"id":8,"rating":5},{"id":9,"rating":2}]}];

const result = movies
  .flatMap(m => m.movies)
  .filter(m => m.rating > 3)
  .map(m => m.id);

console.log(result);

【讨论】：

【解决方案2】：

您可以使用forEach() 循环：

const movies = [{
  "name": "Actions",
  "movies": [{
    "id": 1,
    "rating": 2
  }, {
    "id": 2,
    "rating": 1
  }, {
    "id": 3,
    "rating": 4
  }]
}, {
  "name": "Comedy",
  "movies": [{
    "id": 4,
    "rating": 3
  }, {
    "id": 5,
    "rating": 4
  }, {
    "id": 6,
    "rating": 5
  }]
}, {
  "name": "Sci-fi",
  "movies": [{
    "id": 7,
    "rating": 1
  }, {
    "id": 8,
    "rating": 5
  }, {
    "id": 9,
    "rating": 2
  }]
}];

let result = [];

movies.forEach(({movies}) => {
  var movie3 = movies.filter(({rating}) => rating > 3).map(({id}) => id);
  result = [...result, ...movie3];
});
console.log(result);

【讨论】：

这只是.map()的“复杂”方式

【解决方案3】：

你可以在flat函数后面加上map(rw => rw.id)得到想要的输出。

let res = movies
          .map( m => m.movies
                    .filter( f => f.rating > 3 ) 
          )
          .flat().map(rw => rw.id);
console.log(res);

【讨论】：