Scala - Tuples


Advertisements


Scala tuple combines a fixed number of items together so that they can be passed around as a whole. Unlike an array or list, a tuple can hold objects with different types but they are also immutable.

The following is an example of a tuple holding an integer, a string, and the console.

val t = (1, "hello", Console)

Which is syntactic sugar (short cut) for the following −

val t = new Tuple3(1, "hello", Console)

The actual type of a tuple depends upon the number and of elements it contains and the types of those elements. Thus, the type of (99, "Luftballons") is Tuple2[Int, String]. The type of ('u', 'r', "the", 1, 4, "me") is Tuple6[Char, Char, String, Int, Int, String]

Tuples are of type Tuple1, Tuple2, Tuple3 and so on. There currently is an upper limit of 22 in the Scala if you need more, then you can use a collection, not a tuple. For each TupleN type, where 1 <= N <= 22, Scala defines a number of element-access methods. Given the following definition −

val t = (4,3,2,1)

To access elements of a tuple t, you can use method t._1 to access the first element, t._2 to access the second, and so on. For example, the following expression computes the sum of all elements of t.

val sum = t._1 + t._2 + t._3 + t._4

You can use Tuple to write a method that takes a List[Double] and returns the count, the sum, and the sum of squares returned in a three-element Tuple, a Tuple3[Int, Double, Double]. They are also useful to pass a list of data values as messages between actors in concurrent programming.

Try the following example program. It shows how to use a tuple.

Example

object Demo {
   def main(args: Array[String]) {
      val t = (4,3,2,1)
      val sum = t._1 + t._2 + t._3 + t._4

      println( "Sum of elements: "  + sum )
   }
}

Save the above program in Demo.scala. The following commands are used to compile and execute this program.

Commands

\>scalac Demo.scala
\>scala Demo

Output

Sum of elements: 10

Iterate over the Tuple

You can use Tuple.productIterator() method to iterate over all the elements of a Tuple.

Try the following example program to iterate over tuples.

Example

object Demo {
   def main(args: Array[String]) {
      val t = (4,3,2,1)
      
      t.productIterator.foreach{ i =>println("Value = " + i )}
   }
}

Save the above program in Demo.scala. The following commands are used to compile and execute this program.

Commands

\>scalac Demo.scala
\>scala Demo

Output

Value = 4
Value = 3
Value = 2
Value = 1

Converting to String

You can use Tuple.toString() method to concatenate all the elements of the tuple into a string. Try the following example program to convert to String.

Example

object Demo {
   def main(args: Array[String]) {
      val t = new Tuple3(1, "hello", Console)
      
      println("Concatenated String: " + t.toString() )
   }
}

Save the above program in Demo.scala. The following commands are used to compile and execute this program.

Command

\>scalac Demo.scala
\>scala Demo

Output

Concatenated String: (1,hello,scala.Console$@281acd47)

Swap the Elements

You can use Tuple.swap method to swap the elements of a Tuple2.

Try the following example program to swap the elements.

Example

object Demo {
   def main(args: Array[String]) {
      val t = new Tuple2("Scala", "hello")
      
      println("Swapped Tuple: " + t.swap )
   }
}

Save the above program in Demo.scala. The following commands are used to compile and execute this program.

Command

\>scalac Demo.scala
\>scala Demo

Output

Swapped tuple: (hello,Scala)

scala_collections.htm

Advertisements