Scala 'map' method: examples and syntax (List, Vector, Seq)

As a quick note today, in this post I’ll share some examples of the Scala map method as it works on sequences like the List, Vector, and Seq classes.

map == transform

Basically you can think of map as meaning transform: it lets you transform one collection into another. For instance, these examples in the Scala REPL show how to transform a list of strings into a list of integers, where the integers correspond to the length of each string:

scala> val names = List("Kim", "Julia", "Adam")
val names: List[String] = List(Kim, Julia, Adam)

scala> val nameLengths = names.map(name => name.length)
val nameLengths: List[Int] = List(3, 5, 4)

scala> val nameLengths = names.map(_.length)
val nameLengths: List[Int] = List(3, 5, 4)

As those examples show, the map method transforms the first list — List("Kim", "Julia", "Adam") — into the second list — List(3, 5, 4).

Another map method example

Here’s another example that transforms the lowercase names in the first list into the capitalized names in the second list:

scala> val lcNames = Vector("kim", "julia", "adam")
val lcNames: Vector[String] = Vector(kim, julia, adam)

scala> val ucNames = lcNames.map(_.capitalize)
val ucNames: Vector[String] = Vector(Kim, Julia, Adam)

Finally, here’s another example that shows how to multiply each number in one list to create another:

scala> val xs = Seq(1, 2, 3)
val xs: Seq[Int] = List(1, 2, 3)

scala> val ys = xs.map(_ * 2)
val ys: Seq[Int] = List(2, 4, 6)

The Scala map method is equivalent to a simple for/yield expression

If it helps, you can think of the Scala map method as being a replacement for for/yield loops. For instance, that last example is equivalent to this much longer expression in Scala 3:

val xs = Seq(1, 2, 3)
val ys = 
    for
        x <- xs
    yield
        x * 2

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Summary

In summary, if you wanted to see how to use the Scala map method, I hope these examples that use sequences like List, Vector, and Seq are helpful.