Question

我有一系列事件对象，如下所示：

{
    date: "2015-06-03T19:29:01.000Z",
    description: "Test",
    talks: [{
        author: "Nick",
        tags: ["tag1", "tag2", "tag3"]
    }]
}

我只想从这个对象中获取标签，所以我像这样使用Ramda：

let eventTags = pipe(prop('talks'), map(prop('tags')), flatten, uniq)
... 
eventTags(event); //and call function on event object

但是有时事件对象看起来像这样：

{
    date: "2015-06-03T19:29:01.000Z",
    description: "Test",
    talks: [{
        author: "Nick",
        tags: null
    }]
}

所以我在[null]数组中得到了eventTags，但我希望得到一个空数组。那么如何过滤null？

Answer 1

我会提倡使用镜头访问tags并使用 Ramda 和Sanctuary将undefined视为Maybe Nothing的解决方案

const x = [{
  date: "2015-06-03T19:29:01.000Z",
  description: "Test",
  talks: [{
    author: "Nick",
    tags: ["tag1", "tag2", "tag3"]
  }]
}, {
  date: "2015-06-03T19:29:01.000Z",
  description: "Test",
  talks: [{
    author: "Nick",
    tags: null
  }]
}]

const viewTalks = S.compose ( S.toMaybe ) ( 
  R.view ( R.lensProp( 'talks' ) ) 
)

const viewTags = S.compose ( S.toMaybe ) ( 
  R.view ( R.lensProp ( 'tags' ) ) 
)

const allTalkTags = S.map ( S.pipe ( [
  S.map ( viewTags ),
  S.justs,
  R.unnest
] ) )

const allTalksTags = S.pipe( [
  S.map ( S.pipe( [
    viewTalks,
    allTalkTags
  ] ) ),
  S.justs,
  R.unnest,
  R.uniq
] )

// outputs: ['tag1', 'tag2', 'tag3']
allTalksTags ( x )

Click to run a working sample

Answer 2

如果接收到null或未定义的值，您可以在此处使用R.defaultTo([])来创建一个返回空数组的函数，否则将值传递给未修改的。

const eventTags = pipe(
  prop('talks'),
  map(pipe(prop('tags'), defaultTo([]))),
  flatten,
  uniq
)

Answer 3

通过MatíasFidemraizer帮助我将eventTags功能更改为：

const viewTags = talk => !!talk.tags ? talk.tags : [];

export let eventTags = pipe(prop('talks'), map(viewTags), flatten, uniq)

Ramda过滤器null prop

3 个答案: