CODEWITHSUNDEEP
scala
mthmulders
mthmulders

Reputation: 9705

Decompose Scala sequence into member values

I'm looking for an elegant way of accessing two items in a Seq at the same time. I've checked earlier in my code that the Seq will have exactly two items. Now I would like to be able to give them names, so they have meaning.

records
  .sliding(2) // makes sure we get `Seq` with two items
  .map(recs => {
    // Something like this...
    val (former, latter) = recs       
  })

Is there an elegant and/or idiomatic way to achieve this in Scala?

Upvotes: 1

Views: 1083

Answers (5)

Tim
Tim

Reputation: 27356

I'm not sure if it is any more elegant, but you can also unpick the sequence like this:

val former +: latter +: _ = recs

Upvotes: 3

Shaido
Shaido

Reputation: 28322

The result of sliding is a List. Using a pattern match, you can give name to these elements like this:

map{ case List(former, latter) => 
  ...
}

Note that since it's a pattern match, you need to use {} instead of ().

Upvotes: 1

user unknown
user unknown

Reputation: 36229

For a records of known types (for example, Int):

records.sliding (2).map (_ match { 
  case List (former:Int, latter:Int) => former + latter })

Note, that this will unify element (0, 1), then (1, 2), (2, 3) ... and so on. To combine pairwise, use sliding (2, 2): 

val pairs = records.sliding (2, 2).map (_ match { 
  case List (former: Int, latter: Int) => former + latter
  case List (one: Int) => one 
}).toList

Note, that you now need an extra case for just one element, if the records size is odd.

Upvotes: 0

Jens Hoffmann
Jens Hoffmann

Reputation: 6801

You can use pattern matching to decompose the structure of your list:

val records = List("first", "second")

records match {
    case first +: second +: Nil => println(s"1: $first, 2: $second")
    case _                      => // Won't happen (you can omit this)
}

will output

1: first, 2: second

Upvotes: 1

Maroun
Maroun

Reputation: 95948

You can access the elements by their index:

map { recs => {
    val (former, latter) = recs(0), recs(1)       
}}

Upvotes: 1

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