Lambda Expression in Scala

Lambda Expression refers to an expression that uses an anonymous function instead of variable or value. Lambda expressions are more convenient when we have a simple function to be used in one place. These expressions are faster and more expressive than defining a whole function. We can make our lambda expressions reusable for any kind of transformations. It can iterate over a collection of objects and perform some kind of transformation to them.
Syntax:

val lambda_exp = (variable:Type) => Transformation_Expression

Example:

// lambda expression to find double of x
val ex = (x:Int) => x + x

Working With Lambda Expressions

• We can pass values to a lambda just like a normal function call.
  Example :

  // Scala program to show
  // working of lambda expression
  
  // Creating object
  object GfG
  {
  
  // Main method
  def main(args:Array[String])
  {
      // lambda expression
      val ex1 = (x:Int) => x + 2
  
      // with multiple parameters
      val ex2 = (x:Int, y:Int) => x * y
  
      println(ex1(7))
      println(ex2(2, 3))
  }
  }

  Output:

  9
  6

• To apply transformation to any collection, we generally use map() function. It is a higher-order function where we can pass our lambda as a parameter in order to transform every element of the collection according to the definition of our lambda expression.
  Example :

  // Scala program to apply
  // transformation on collection
  
  // Creating object
  object GfG
  {
  
  // Main method
  def main(args:Array[String])
  {
      // list of numbers
      val l = List(1, 1, 2, 3, 5, 8)
  
      // squaring each element of the list
      val res = l.map( (x:Int) => x * x )
  
  /* OR
  val res = l.map( x=> x * x )
  */
      println(res)
  }
  }

  Output:

  List(1, 1, 4, 9, 25, 64)

  We can see that the defined anonymous function to perform the square operation is not reusable.

• We are passing it as an argument. However, we can make it reusable and may use it with different collections.
  Example :

  // Scala program to apply
  // transformation on collection
  
  // Creating object
  object GfG
  {
      // Main method
      def main(args:Array[String])
      {
          // list of numbers
          val l1 = List(1, 1, 2, 3, 5, 8)
          val l2 = List(13, 21, 34)
  
          // reusable lambda
          val func = (x:Int) => x * x
  
          // squaring each element of the lists
          val res1 = l1.map( func )
          val res2 = l2.map( func )
  
          println(res1)
          println(res2)
      }
  }

  Output:

  List(1, 1, 4, 9, 25, 64)
  List(169, 441, 1156)

• A lambda can also be used as a parameter to a function.
  Example :

  // Scala program to pass lambda
  // as parameter to a function
  
  // Creating object
  object GfG
  {
  
      // transform function with integer x and
      // function f as parameter
      // f accepts Int and returns Double
      def transform( x:Int, f:Int => Double)
      =
      f(x)
  
      // Main method
      def main(args:Array[String])
      {
  
          // lambda is passed to f:Int => Double
          val res = transform(2, r => 3.14 * r * r)
  
          println(res)
  }
  }

  Output:

  12.56

  In above example, transform function accepts integer x and function f, applies the transformation to x defined by f. Lambda passed as the parameter in function call returns Double type. Therefore, parameter f must obey the lambda definition.

• We can perform the same task on any collection as well. In case of collections, the only change we need to make in transform function is using map function to apply transformation defined by f to every element of the list l.
  Example :

  // Scala program to pass lambda
  // as parameter to a function
  
  // Creating object
  object GfG
  {
  
      // transform function with integer list l and
      // function f as parameter
      // f accepts Int and returns Double
      def transform( l:List[Int], f:Int => Double)
      =
      l.map(f)
  
      // Main method
      def main(args:Array[String])
      {
          // lambda is passed to f:Int => Double
          val res = transform(List(1, 2, 3), r => 3.14 * r * r)
          println(res)
      }
  }

  Output:

  List(3.14, 12.56, 28.259999999999998)