访问更高阶函数内的数组对象

Question

我正在尝试访问我在其中使用reduce函数的数组的长度,但是我似乎无法做到,有没有人知道是否可以访问数组任何高阶函数内的对象？

PS:我试过this但没有成功;

PSS:我想使用reduce函数计算平均评级,所以我使用reduce来对数组中的所有值求和,并将这些相同的值除以数组长度,如下所示:

let averageRating = watchList
    .filter(movie => movie.Director === 'Christopher Nolan')
    .map(x => parseFloat(x.imdbRating))
    .reduce((total, current) => total + (current / 'array length'));

你猜对了'数组长度',数组长度.

PSSS:试过

var averageRating = watchList
  .filter(movie => movie.Director === 'Christopher Nolan')
  .map(x => parseFloat(x.imdbRating))
  .reduce((total, current, index, arr) => total + (current / arr.length));

但是数组长度随着数组的减少而不断变化,所以它不适用于我的目的.

Answer 1

这应该可以做到：

let averageRating = watchList
    .filter(movie => movie.Director === 'Christopher Nolan')
    .map(x => parseFloat(x.imdbRating))
    .reduce((total, current, idx, arr) => total + (current / arr.length));

更新

如果您有兴趣了解我将如何在我喜欢的库Ramda中执行此操作（免责声明：我是其主要作者之一），代码将如下所示：

let averageRating = watchList
    .filter(movie => movie.Director === 'Christopher Nolan')
    .map(x => parseFloat(x.imdbRating))
    .reduce((total, current, idx, arr) => total + (current / arr.length));

const {pipe, filter, propEq, pluck, map, mean} = R;

const watchList = [{"Director": "Christopher Nolan", "imdbRating": 4.6, "title": "..."}, {"Director": "Michel Gondry", "imdbRating": 3.9, "title": "..."}, {"Director": "Christopher Nolan", "imdbRating": 2.8, "title": "..."}, {"Director": "Christopher Nolan", "imdbRating": 4.9, "title": "..."}, {"Director": "Alfred Hitchcock", "imdbRating": 4.6, "title": "..."}, {"Director": "Christopher Nolan", "imdbRating": 4.6, "title": "..."}];

const averageRating = pipe(
  filter(propEq('Director', 'Christopher Nolan')),
  pluck('imdbRating'),
  map(Number),
  mean
);

console.log(averageRating(watchList));

我发现这会产生非常干净、可读的代码。