Collections

Vector Indexing

Read a value from a vector by index.

vector-indexing A vector supports index reads. Index zero reads the first element.

Vector Indexing

index
VectorIndexing.scala
Replay: real traced execution (multi-file project)
object Main {
  def main(args: Array[String]): Unit = {
    val index = 1
    val colors = Vector("red", "green", "blue")
    val chosen = colors(index)

    println("index=" + index)
    println("chosen=" + chosen)
  }
}

object Main {
  def main(args: Array[String]): Unit = {
    val index = 0
    val colors = Vector("red", "green", "blue")
    val chosen = colors(index)

    println("index=" + index)
    println("chosen=" + chosen)
  }
}

object Main {
  def main(args: Array[String]): Unit = {
    val index = 2
    val colors = Vector("red", "green", "blue")
    val chosen = colors(index)

    println("index=" + index)
    println("chosen=" + chosen)
  }
}

  1. index ← 1, colors ← Vector(red, green, blue), chosen ← green

    1object Main {2  def main(args: Array[String]): Unit = {3    val index→ 1 = 1 //@index=0, 24    val colors→ Vector(red, green, blue) = Vector("red", "green", "blue")5    val chosen→ green = colors(index)green67    println("index=" + index1)8    println("chosen=" + chosengreen)9  }10}
    outputindex=1
chosen=green

  1. index ← 0, colors ← Vector(red, green, blue), chosen ← red

    1object Main {2  def main(args: Array[String]): Unit = {3    val index→ 0 = 04    val colors→ Vector(red, green, blue) = Vector("red", "green", "blue")5    val chosen→ red = colors(index)red67    println("index=" + index0)8    println("chosen=" + chosenred)9  }10}
    outputindex=0
chosen=red

  1. index ← 2, colors ← Vector(red, green, blue), chosen ← blue

    1object Main {2  def main(args: Array[String]): Unit = {3    val index→ 2 = 24    val colors→ Vector(red, green, blue) = Vector("red", "green", "blue")5    val chosen→ blue = colors(index)blue67    println("index=" + index2)8    println("chosen=" + chosenblue)9  }10}
    outputindex=2
chosen=blue

Pick by Index

  1. The vector stores red, green, and blue.
  2. Scala indexes start at 0.
  3. index is 1.
  4. colors(index) selects green. | Index | Color | Selected? | | --- | --- | --- | | 0 | red | no | | 1 | green | yes | | 2 | blue | no |

Exercise: VectorIndexing.scala

Pick one vector color by index and print the index and chosen color