groupBy和sortBy本机ES6中的对象数组

Question

我们有一个对象数组，我们需要按组ID对这些对象进行分组。

然后我们需要通过时间戳获取一个带有已排序组的数组。

这是最初的集合：

const arr = [
  {id: 'id1', group: '123', timestamp: 222},
  {id: 'id2', group: '123', timestamp: 999 },
  {id: 'id3', group: '456', timestamp: 333 },
  {id: 'id4', group: '789', timestamp: 111 },
  {id: 'id5', group: '554', timestamp: 555 },
];

我们试图获得的结果是：

result = [
  [
    {id: 'id4', group: '789', timestamp: 111 }, 
  ],
  [
    {id: 'id1', group: '123', timestamp: 222},
    {id: 'id2', group: '123', timestamp: 999 },
  ],
  [
    {id: 'id3', group: '456', timestamp: 333 },
  ],
  [
    {id: 'id5', group: '554', timestamp: 555 },
  ]
]

我们使用Underscore.js实现了这一点，但我们正在寻找使用原生javascript的解决方案，并且我们努力从简化对象传递到数组数组。

var groups = _(arr).chain()
    .groupBy("group")
    .sortBy((data) => _.first(data).timestamp)
    .value();

https://jsfiddle.net/tdsow1ph/

我们尝试首先使用这样的方法对项目进行分组：

const groupBy = (arr, propertyToGroupBy) => {
    return arr.reduce((groups, item) => {
      const val = item[propertyToGroupBy];

      groups[val] = groups[val] || [];
      groups[val].push(item);

      return groups;
    }, {});
  }

但是我们获得了一个难以理解的对象。 因此我们需要将其转换为数组数组，但我们很难做到这一点，然后对时间戳值应用排序。

Answer 1

您可以使用reduce()将组作为键将数组分组到对象中。 使用Object.values()将对象转换为数组。

 const arr = [{"id":"id1","group":"123","timestamp":222},{"id":"id2","group":"123","timestamp":999},{"id":"id3","group":"456","timestamp":333},{"id":"id4","group":"789","timestamp":111},{"id":"id5","group":"554","timestamp":555}]; var result = Object.values(arr.reduce((c, v) => { c[v.group] = c[v.group] || []; c[v.group].push(v); return c; }, {})); console.log(result); 

使用sort()

 const arr = [{"id":"id4","group":"789","timestamp":111},{"id":"id1","group":"123","timestamp":222},{"id":"id3","group":"456","timestamp":333},{"id":"id5","group":"554","timestamp":555},{"id":"id2","group":"123","timestamp":999}] var result = Object.values( arr .sort((a, b) => a.timestamp - b.timestamp) .reduce((c, v) => { c[v.group] = c[v.group] || []; c[v.group].push(v); return c; }, {}) ); console.log(result); 

Answer 2

这是ES6中使用Map对象和reduce的另一个单行实现：

 const arr = [ {id: 'id1', group: '123', timestamp: 222}, {id: 'id2', group: '123', timestamp: 999 }, {id: 'id3', group: '456', timestamp: 333 }, {id: 'id4', group: '789', timestamp: 111 }, {id: 'id5', group: '554', timestamp: 555 }, ]; const result = [...arr.reduce((r,c) => (r.set(c.group, r.has(c.group) ? [...r.get(c.group), c] : [c]), r), new Map()).values()] console.log(result) 

对于排序只是通过初始sort减少的前缀：

 const arr = [ {id: 'id1', group: '123', timestamp: 222}, {id: 'id2', group: '123', timestamp: 999 }, {id: 'id3', group: '456', timestamp: 333 }, {id: 'id4', group: '789', timestamp: 111 }, {id: 'id5', group: '554', timestamp: 555 }, ]; const result = [...arr.sort((a,b) => a.timestamp - b.timestamp) .reduce((r,c) => (r.set(c.group, r.has(c.group) ? [...r.get(c.group), c] : [c]), r), new Map()).values()] console.log(result)