I have array of event objects, looks like:

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

I want to take only tags from this object, so I use Ramda like this:

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

But there is cases when event object looks like this:

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

So I got [null] in my eventTags array, but I want to get an empty array instead. So how can I filter null?

I have array of event objects, looks like:

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

I want to take only tags from this object, so I use Ramda like this:

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

But there is cases when event object looks like this:

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

So I got [null] in my eventTags array, but I want to get an empty array instead. So how can I filter null?

• javascript
• ramda.js

• No need to use Ramda, just do event.talks.tags || []. – str Commented Apr 10, 2018 at 8:57
• My mistake - talks is array of objects – Mad Max Commented Apr 10, 2018 at 9:04

3 Answers 3

You could utilise R.defaultTo([]) here to create a function that returns an empty array if null or undefined values are received, otherwise passing the value through unmodified.

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

I would advocate for a solution that could access tags using lenses and treat undefined as Maybe Nothing using both Ramda and Sanctuary

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.pose ( S.toMaybe ) ( 
  R.view ( R.lensProp( 'talks' ) ) 
)

const viewTags = S.pose ( 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

With Matías Fidemraizer help I changed my eventTags function to this:

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

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