CODEWITHSUNDEEP
scalalist
Rupesh Kumar
Rupesh Kumar

Reputation: 29

List building in Scala

Can anyone explain in detail what this function is doing and what is the use of scala.collection.mutable.ListBuffer.empty[Int]?

def f(num: Int, arr: List[Int]): List[Int] = {
  val l = scala.collection.mutable.ListBuffer.empty[Int]
  arr.foreach(i => {
    println(i)
    (1 to num).foreach(_ => l += i)
  })

  l.toList
}

Upvotes: 0

Views: 98

Answers (1)

Nagarjuna Pamu
Nagarjuna Pamu

Reputation: 14825

ListBuffer.empty[Int] is used for instantiating the ListBuffer

ListBuffer.empty[Int] is same as ListBuffer[Int]()

ListBuffer is mutable list.

  1. For every value i of arr list.
  2. i is printed
  3. num times i is added to list buffer

Later the mutable list is converted to immutable list using toList call

That means

every value of arr list is added to list buffer num times

# Scala REPL

scala> :paste
// Entering paste mode (ctrl-D to finish)

def f(num: Int, arr: List[Int]): List[Int] = {
  val l = scala.collection.mutable.ListBuffer.empty[Int]
  arr.foreach(i => {
    println(i)
    (1 to num).foreach(_ => l += i)
  })

  l.toList
}

// Exiting paste mode, now interpreting.

f: (num: Int, arr: List[Int])List[Int]

scala> f(10, (1 to 10).toList)
1
2
3
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5
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7
8
9
10
res2: List[Int] = List(1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10)

Upvotes: 1

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