使用Array#reduce汇总对象数组中的出现次数

问题描述

我想总结一个对象数组，并返回另一个对象数组中对象出现的次数.最好的方法是什么?

I want to summarize an array of objects and return the number of object occurrences in another array of objects. What is the best way to do this?

从此

var arrayOfSongs = [
  {"title":"Blue","duration":161.71,"audioUrl":"/assets/music/blue","playing":false,"playedAt":"2016-12-21T22:58:55.203Z"},
  {"title":"Blue","duration":161.71,"audioUrl":"/assets/music/blue","playing":false,"playedAt":"2016-12-21T22:58:55.203Z"},
  {"title":"Blue","duration":161.71,"audioUrl":"/assets/music/blue","playing":false,"playedAt":"2016-12-21T22:58:55.203Z"},
  {"title":"Green","duration":161.71,"audioUrl":"/assets/music/blue","playing":false,"playedAt":"2016-12-21T22:58:55.203Z"}
];

对此

var newArrayOfSongs = [
  {"title": "Blue", "playCount": 3 },
  {"title": "Green", "playCount": 1}
]

我尝试过

 arrayOfSongs.reduce(function(acc, cv) {
   acc[cv.title] = (acc[cv.title] || 0) + 1;
     return acc;
   }, {});
 }

但是它返回一个对象:

 { "Blue": 3, "Green": 1};

推荐答案

您应将初始参数作为数组而不是对象和过滤器数组传递给reduce函数，如下所示，以获取现有值，

You should pass the initial argument to the reduce function as an array instead of object and filter array for the existing value as below,

有效代码段:

var arrayOfSongs = [
  {"title":"Blue","duration":161.71,"audioUrl":"/assets/music/blue","playing":false,"playedAt":"2016-12-21T22:58:55.203Z"},
  {"title":"Blue","duration":161.71,"audioUrl":"/assets/music/blue","playing":false,"playedAt":"2016-12-21T22:58:55.203Z"},
  {"title":"Blue","duration":161.71,"audioUrl":"/assets/music/blue","playing":false,"playedAt":"2016-12-21T22:58:55.203Z"},
  {"title":"Green","duration":161.71,"audioUrl":"/assets/music/blue","playing":false,"playedAt":"2016-12-21T22:58:55.203Z"}
];


var newArrayOfSongs = arrayOfSongs.reduce(function(acc, cv) {
    var arr = acc.filter(function(obj) {
      return obj.title === cv.title;
    });

    if(arr.length === 0) {
      acc.push({title: cv.title, playCount: 1});
    } else {
      arr[0].playCount += 1;
    }

    return acc;
   }, []);

console.log(newArrayOfSongs);

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