Scala - printing arrays

Question

It seems like the support for printing arrays is somewhat lacking in Scala. If you print one, you get the default garbage you'd get in Java:

scala> val array = Array.fill(2,2)(0)             
array: Array[Array[Int]] = Array(Array(0, 0), Array(0, 0))

scala> println(array)
[[I@d2f01d

Furthermore, you cannot use the Java toString/deepToString methods from the java.util.Arrays class: (or at least I cannot figure it out)

scala> println(java.util.Arrays.deepToString(array))
<console>:7: error: type mismatch;
 found   : Array[Array[Int]]
 required: Array[java.lang.Object]
       println(java.util.Arrays.deepToString(array))

The best solution I could find for printing a 2D array is to do the following:

scala> println(array.map(_.mkString(" ")).mkString("\n"))
0 0
0 0

Is there a more idiomatic way of doing this?

Answer 1

In Scala 2.8, you can use the deep method defined on Array, that returns an IndexedSeq cointaining all of the (possibly nested) elements of this array, and call mkString on that:

scala> val array = Array.fill(2,2)(0)
array: Array[Array[Int]] = Array(Array(0, 0), Array(0, 0))

scala> println(array.deep.mkString("\n"))
Array(0, 0)
Array(0, 0)

The IndexedSeq returned does have a stringprefix 'Array' by default, so I'm not sure whether this gives precisely what you wanted.

Answer 2

How about this:

scala> val array = Array.fill(2,2)(0)
array: Array[Array[Int]] = Array(Array(0, 0), Array(0, 0))

scala> import scala.runtime.ScalaRunTime._
import scala.runtime.ScalaRunTime._

scala> val str = stringOf(array)
str: String =
Array(Array(0, 0), Array(0, 0))

Answer 3

Adding little more to Arjan's answer - you can use the mkString method to print and even specify the separator between elements. For instance :

val a = Array(1, 7, 2, 9)
a.mkString(" and ")
// "1 and 7 and 2 and 9"
a.mkString("<", ",", ">") //mkString(start: String, sep: String, end: String)
// "<1,7,2,9>" 

Answer 4

Try simply this:

  // create an array
  val array1 = Array(1,2,3)
  // print an array elements seperated by comma
  println(array1.mkString(","))
  // print an array elements seperated by a line
  println(array1.mkString("\n"))

  // create a function
  def printArray[k](a:Array[k])= println(a.mkString(","))
  printArray(array1)

Answer 5

我比较喜欢这个：

Array(1, 7, 2, 9).foreach(println)

Answer 6

You can get neat formatting of Array[Array[Somethings]] with custom separators for the inner as well as the outer array follows:

    def arrayToString(a: Array[Array[Int]]) : String = {
       val str = for (l <- a) yield l.mkString("{", ",", "}")
       str.mkString("{",",\n","}")
    }

    val foo = Array.fill(2,2)(0)
    println(arrayToString(foo))

This results in:

    {{0,0},
    {0,0}}

Answer 7

The "functional programming" way to do this (as far as I concern) is:

scala> array foreach{case a => a foreach {b => print(b.toString + " ")}; print('\n')}
0 0 
0 0 

Or if you don't really care about the spacing:

scala> array foreach{a => a foreach println}
0
0
0
0

IMHO, functional programming can get a little messy, if it takes too long to make this, I'd say just go with the imperative way.

Answer 8

Array(1, 7, 2, 9) foreach println

Minor modification of rupert160's answer. No need for dots or parenthesis.