The Vector Class

The Vector class is an indexed, immutable sequence. The “indexed” part of the description means that you can access Vector elements very rapidly by their index value, such as accessing listOfPeople(999999).

In general, except for the difference that Vector is indexed and List is not, the two classes work the same, so we’ll run through these examples quickly.

Here are a few ways you can create a Vector:

val nums = Vector(1, 2, 3, 4, 5)

val strings = Vector("one", "two")

val peeps = Vector(
    Person("Bert"),
    Person("Ernie"),
    Person("Grover")
)

Because Vector is immutable, you can’t add new elements to it. Instead you create a new sequence by appending or prepending elements to an existing Vector. For instance, given this Vector:

val a = Vector(1,2,3)

you append elements like this:

val b = a :+ 4

and this:

val b = a ++ Vector(4, 5)

The REPL shows how this works:

scala> val a = Vector(1,2,3)
a: Vector[Int] = Vector(1, 2, 3)

scala> val b = a :+ 4
b: Vector[Int] = Vector(1, 2, 3, 4)

scala> val b = a ++ Vector(4, 5)
b: Vector[Int] = Vector(1, 2, 3, 4, 5)

You can also prepend elements like this:

val b = 0 +: a

and this:

val b = Vector(-1, 0) ++: a

Once again the REPL shows how this works:

scala> val b = 0 +: a
b: Vector[Int] = Vector(0, 1, 2, 3)

scala> val b = Vector(-1, 0) ++: a
b: Vector[Int] = Vector(-1, 0, 1, 2, 3)

Because Vector is not a linked-list (like List), you can prepend and append elements to it, and the speed of both approaches should be similar.

Finally, you loop over elements in a Vector just like you do with an ArrayBuffer or List:

scala> val names = Vector("Joel", "Chris", "Ed")
val names: Vector[String] = Vector(Joel, Chris, Ed)

scala> for (name <- names) println(name)
Joel
Chris
Ed