Scala Cookbook

2.8. Creating a Range, List, or Array of Numbers

Problem

You need to create a range, list, or array of numbers, such as in a for loop, or for testing purposes.

Solution

Use the to method of the Int class to create a Range with the desired elements:

scala> val r = 1 to 10
r: scala.collection.immutable.Range.Inclusive = Range(1, 2, 3, 4, 5,
   6, 7, 8, 9, 10)

You can set the step with the by method:

scala> val r = 1 to 10 by 2
r: scala.collection.immutable.Range = Range(1, 3, 5, 7, 9)

scala> val r = 1 to 10 by 3
r: scala.collection.immutable.Range = Range(1, 4, 7, 10)

Ranges are commonly used in for loops:

scala> for (i <- 1 to 5) println(i)
1
2
3
4
5

When creating a Range, you can also use until instead of to:

scala> for (i <- 1 until 5) println(i)
1
2
3
4

Discussion

Scala makes it easy to create a range of numbers. The first three examples shown in the Solution create a Range. You can easily convert a Range to other sequences, such as an Array or List, like this:

scala> val x = 1 to 10 toArray
x: Array[Int] = Array(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)

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

Although this infix notation syntax is clear in many situations (such as for loops), it’s generally preferable to use this syntax:

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

scala> val x = (1 to 10).toArray
x: Array[Int] = Array(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)

The magic that makes this process work is the to and until methods, which you’ll ...