How to create a Range, List, or Array of numbers in Scala

Scala FAQ: How can I create a range, list, or array of numbers in Scala, such as in aforloop, or for testing purposes?

Solution

Use thetomethod of theIntclass to create aRangewith 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 also set the step with thebymethod:

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)

Note that ranges are commonly used inforloops:

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

1
2
3
4
5

When creating aRange, you can also useuntilinstead ofto:

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 aRange. You can easily convert aRangeto other sequences, such as anArrayorList, 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 asforloops), 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 thetoanduntilmethods, which you’ll find in theRichIntclass. When you type the following portion of the code, you’re actually invoking thetomethod of theRichIntclass:

1 to

You can demonstrate thattois a method on anIntby using this syntax in the REPL:

1.to(10)

Although the infix notation (1 to 10) shown in most of these examples can make your code more readable,Rahul Phulore has a post on Stack Overflowwhere he advises against using it for anything other than internal DSLs.

Combine this with Recipe 2.7 of the Scala Cookbook, “Generating Random Numbers,” and you can create a_random length_range, which can be useful for testing:

scala>var range = 0 to scala.util.Random.nextInt(10)

range: scala.collection.immutable.Range.Inclusive = Range(0, 1, 2, 3)

By using a range with the for/yield construct, you don’t have to limit your ranges to sequential numbers:

scala> for (i <- 1 to 5) yield i * 2

res0: scala.collection.immutable.IndexedSeq[Int] = Vector(2, 4, 6, 8, 10)

You also don’t have to limit your ranges to just integers:

scala> for (i <- 1 to 5) yield i.toDouble

res1: scala.collection.immutable.IndexedSeq[Double] = Vector(1.0, 2.0, 3.0, 4.0, 5.0)