Get head item and tail items from scala list

Question

Is there a method in scala to get the (single) head element of a List or Seq and the (collection) tail of the list? I know there\'s

def splitAt(n: Int): (Lis         


        

Answer 1

The tail method returns a collection consisting of all elements except the first one (which is basically the head).

+------------------+------------------------+-------------------------------+
|      Input       |          head          |             tail              |
+------------------+------------------------+-------------------------------+
| List()           | NoSuchElementException | UnsupportedOperationException |
| List(1)          | 1                      | List()                        |
| List(1, 2, 3, 4) | 1                      | List(2, 3, 4)                 |
| ""               | NoSuchElementException | UnsupportedOperationException |
| "A"              | 'A' (char)             | ""                            |
| "Hello"          | 'H'                    | "ello"                        |
+------------------+------------------------+-------------------------------+

Note that the two methods apply to String type as well.

Answering @Leandro question: Yes we can do that, as shown below:

scala> var a::b::c = List("123", "foo", 2020, "bar")
a: Any = 123
b: Any = foo
c: List[Any] = List(2020, bar)

scala> var a::b::c = List("123", "foo", "bar")
a: String = 123
b: String = foo
c: List[String] = List(bar)

scala> var a::b::c = List("123", "foo")
a: String = 123
b: String = foo
c: List[String] = List()

Answer 2

You can use pattern matching:

val hd::tail = List(1,2,3,4,5)
//hd: Int = 1
//tail: List[Int] = List(2, 3, 4, 5) 

Or just .head/.tail methods:

val hd = foo.head
// hd: Int = 1
val hdOpt = foo.headOption
// hd: Option[Int] = Some(1)
val tl = foo.tail
// tl: List[Int] = List(2, 3, 4)