如何按fromCurrencyId、toCurrencyId多字段拆分对象数组？

问题场景 #

我有一个包含大量对象的数组，结构如下：

[
  {
    startAt: "2016-01-01 11:35:00",
    fromCurrencyId: "a49cd579-18ea-44cb-8117-86428b64a27a",
    toCurrencyId: "c5a0c46c-c5b5-49a5-9a16-4a829269583e"
  },
  {
    startAt: "2016-01-01 11:40:00",
    fromCurrencyId: "a49cd579-18ea-44cb-8117-86428b64a27a",
    toCurrencyId: "c5a0c46c-c5b5-49a5-9a16-4a829269583e"
  },
  {
    startAt: "2016-01-01 12:00:00",
    fromCurrencyId: "c5a0c46c-c5b5-49a5-9a16-4a829269583e",
    toCurrencyId: "5491dfe0-7d61-407d-b642-7fd3ec905302"
  },
  {
    startAt: "2016-01-01 12:40:00",
    fromCurrencyId: "c5a0c46c-c5b5-49a5-9a16-4a829269583e",
    toCurrencyId: "5491dfe0-7d61-407d-b642-7fd3ec905302"
  },
  {
    startAt: "2016-01-01 11:40:00",
    fromCurrencyId: "a49cd579-18ea-44cb-8117-86428b64a27a",
    toCurrencyId: "5491dfe0-7d61-407d-b642-7fd3ec905302"
  },
  ...
]

预期效果 #

需要按照fromCurrencyId和toCurrencyId两个字段将数组拆分为子数组，最终结果如下：

[
  [
    {
      startAt: "2016-01-01 11:35:00",
      fromCurrencyId: "a49cd579-18ea-44cb-8117-86428b64a27a",
      toCurrencyId: "c5a0c46c-c5b5-49a5-9a16-4a829269583e"
    },
    {
      startAt: "2016-01-01 11:40:00",
      fromCurrencyId: "a49cd579-18ea-44cb-8117-86428b64a27a",
      toCurrencyId: "c5a0c46c-c5b5-49a5-9a16-4a829269583e"
    }
  ],
  [
    {
      startAt: "2016-01-01 12:00:00",
      fromCurrencyId: "c5a0c46c-c5b5-49a5-9a16-4a829269583e",
      toCurrencyId: "5491dfe0-7d61-407d-b642-7fd3ec905302"
    },
    {
      startAt: "2016-01-01 12:40:00",
      fromCurrencyId: "c5a0c46c-c5b5-49a5-9a16-4a829269583e",
      toCurrencyId: "5491dfe0-7d61-407d-b642-7fd3ec905302"
    }
  ],
  [
    {
      startAt: "2016-01-01 11:40:00",
      fromCurrencyId: "a49cd579-18ea-44cb-8117-86428b64a27a",
      toCurrencyId: "5491dfe0-7d61-407d-b642-7fd3ec905302"
    }
  ]
]

我的尝试 #

我尝试用lodash的groupBy方法实现，但没得到预期结果，代码如下：

const props = ['fromCurrencyId', 'toCurrencyId']

const a = _.groupBy(data, function(note){
  return _.find(_.pick(note, props));
});

解决方案 #

方法一：使用Lodash实现 #

之前的问题在于_.find(_.pick(note, props))只返回了第一个属性的值，无法区分两个字段的组合。正确的做法是将两个字段的值拼接成唯一的分组键：

const props = ['fromCurrencyId', 'toCurrencyId'];
// 按双字段组合分组
const groupedObj = _.groupBy(data, item => `${item[props[0]]}-${item[props[1]]}`);
// 将分组对象转换为二维数组，匹配预期结果
const result = Object.values(groupedObj);

方法二：原生JavaScript实现 #

不用Lodash的话，可以用Array.reduce手动完成分组：

const props = ['fromCurrencyId', 'toCurrencyId'];
// 分组为对象结构
const groupedObj = data.reduce((acc, item) => {
  const key = `${item[props[0]]}-${item[props[1]]}`;
  if (!acc[key]) {
    acc[key] = [];
  }
  acc[key].push(item);
  return acc;
}, {});
// 转换为二维数组
const result = Object.values(groupedObj);

内容的提问来源于stack exchange，提问作者andrejuly