ramda.js如何进行groupby、count、sort等操作。

Question

我有一个数据收集，如。

[{"id":1,"score":4},{"id":2,"score":3},{"id":1,"score":4},{"id":2,"score":3},{"id":3,"score":4},{"id":1,"score":3}]

我希望输出的数据是:

[{"id":1,"count":3},{"id":2,"count":2},{"id":3,"count":1}]

有什么办法可以用Ramda.js来实现这个功能吗？

我尝试使用 countBy(prop("id"))但我不知道如何按数量进行排序。

Answer 1

用R.pipe创建一个函数，使用R.countBy来获取一个对象，这个对象的属性是 "id"。{ [id]: count }然后将数据转换为对，用R.map，和R.applySpec生成一个对象数组。然后用R.sortBy对其进行排序。

const { pipe, countBy, prop, toPairs, map, applySpec, head, last, sortBy, descend } = R

const fn = pipe(
  countBy(prop('id')),
  toPairs,
  map(applySpec({
    id: pipe(head, Number), // or just id: head if the id doesn't have to be a number
    count: last,
  })),
  sortBy(descend(prop('count'))), // or ascend
)

const arr = [{"id":1,"score":4},{"id":2,"score":3},{"id":1,"score":4},{"id":2,"score":3},{"id":3,"score":4},{"id":1,"score":3}]

const result = fn(arr)

console.log(result)

<script src="https://cdnjs.cloudflare.com/ajax/libs/ramda/0.27.0/ramda.js"></script>

Answer 2

很明显 countBy 将是解决方案的一部分，如果你使用Ramda。 我就会选择把它管到 toPairs 和 zipObj 来获得最终结果。

const collect = pipe (
  countBy (prop ('id')),
  toPairs,
  map (zipObj (['id', 'count']))
) 

const data = [{id: 1, score: 4}, {id: 2, score: 3}, {id: 1, score: 4}, {id: 2, score: 3}, {id: 3, score: 4},{id: 1, score: 3}]

console .log (collect (data))

<script src="https://cdnjs.cloudflare.com/ajax/libs/ramda/0.27.0/ramda.js"></script>
<script> const {pipe, countBy, prop, toPairs, map, zipObj} = R             </script>

zipObj 接受一个属性名和值的数组，并将它们压缩成一个对象。

Answer 3

在vanillaJS中，你可以简单地使用reduce和Map

const data = [{"id":1,"score":4},{"id":2,"score":3},{"id":1,"score":4},{"id":2,"score":3},{"id":3,"score":4},{"id":1,"score":3}]

const final = [...data.reduce((op,{id,score})=>{
   if(op.has(id)){
    op.set(id, op.get(id)+1)
   } else {
    op.set(id,1)
   }
   return op;
}, new Map()).entries()].map(([id,count])=>({id,count}))

console.log(final)