java.lang.IndexOutOfBoundsException: 1 | Scala

Question

I have this code:

class myFunc{
  def summatory(list: List[Int]): Int= list match{
    case Nil => 0
    case _ => list(1) + summatory(list.tail)
  }
}

But I'm getting this error: "scalac -classpath . -d . main.scala scala -classpath . Main java.lang.IndexOutOfBoundsException: 1"

How can I solve it?

You don't know if the list will have two elements, you want to use 0 rather than 1 to access the first element. Although, you may rather call head and avoid that accident again, or even better you use proper pattern matching: case head :: tail => head + summatory(tail) — Luis Miguel Mejía Suárez
– Luis Miguel Mejía Suárez, Commented Oct 24, 2022 at 13:30

Guru Stron · Accepted Answer · 2022-10-24 13:48:30Z

3

Collection indexes in Scala a zero-based, so quick fix would be to just use element at 0 index (otherwise your code will fail on the recursive call processing the last element):

case _ => list(0) + summatory(list.tail)

But better just use pattern matching:

def summatory(list: List[Int]): Int = list match {
  case x :: xs => x + summatory(xs)
  case Nil     => 0
}

Or in particular case of sum - just use sum:

def summatory(list: List[Int]): Int = list.sum

edited Oct 24, 2022 at 13:48

answered Oct 24, 2022 at 13:38

Guru Stron

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