javascript - 使用 Array#reduce 汇总对象数组中的出现次数

Question

我想汇总一个对象数组，返回对象在另一个对象数组中出现的次数。执行此操作的最佳方法是什么？

来自这里

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}
]

我试过了

 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};

Answer 1

您应该将初始参数作为数组而不是现有值的对象和过滤器数组传递给 reduce 函数，如下所示，

工作片段:

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);