ES6:将两个数组合并为一个对象数组

Question

我有两个数组,我想合并到一个对象数组...

第一个数组是日期(字符串):

let metrodates = [
 "2008-01",
 "2008-02",
 "2008-03",..ect
];

第二个数组是数字:

let figures = [
 0,
 0.555,
 0.293,..ect
]

我想合并它们来制作一个像这样的对象(所以数组项与它们相似的索引相匹配):

let metrodata = [
   {data: 0, date: "2008-01"},
   {data: 0.555, date: "2008-02"},
   {data: 0.293, date: "2008-03"},..ect
];

到目前为止我这样做是这样的:我创建一个空数组然后循环通过前两个数组中的一个来获取索引号(前两个数组的长度相同)...但是有更简单的方法(在ES6中) )？

  let metrodata = [];

  for(let index in metrodates){
     metrodata.push({data: figures[index], date: metrodates[index]});
  }

Answer 1

最简单的方法可能是使用map和索引提供给回调

let metrodates = [
  "2008-01",
  "2008-02",
  "2008-03"
];

let figures = [
  0,
  0.555,
  0.293
];

let output = metrodates.map((date,i) => ({date, data: figures[i]}));

console.log(output);

另一种选择是创建一个通用的zip函数,将两个输入数组合并为一个数组.这通常被称为"拉链",因为它像拉链上的牙齿一样交织输入.

const zip = ([x,...xs], [y,...ys]) => {
  if (x === undefined || y === undefined)
    return [];
  else
    return [[x,y], ...zip(xs, ys)];
}

let metrodates = [
  "2008-01",
  "2008-02",
  "2008-03"
];

let figures = [
  0,
  0.555,
  0.293
];

let output = zip(metrodates, figures).map(([date, data]) => ({date, data}));

console.log(output);

另一个选择是创建一个接受多个源数组的通用映射函数.映射函数将从每个源列表中接收一个值.有关其使用的更多示例,请参阅Racket的映射过程.

这个答案可能看起来最复杂,但它也是最通用的,因为它接受任意数量的源数组输入.

const isEmpty = xs => xs.length === 0;
const head = ([x,...xs]) => x;
const tail = ([x,...xs]) => xs;

const map = (f, ...xxs) => {
  let loop = (acc, xxs) => {
    if (xxs.some(isEmpty))
      return acc;
    else
      return loop([...acc, f(...xxs.map(head))], xxs.map(tail));
  };
  return loop([], xxs);
}

let metrodates = [
  "2008-01",
  "2008-02",
  "2008-03"
];

let figures = [
  0,
  0.555,
  0.293
];

let output = map(
  (date, data) => ({date, data}),
  metrodates,
  figures
);

console.log(output);