Efficient iteration with index in Scala

Question

Since Scala does not have old Java style for loops with index,

// does not work
val xs = Array(\"first\", \"second\", \"third\")
for (i=0; i<         


        

Answer 1

Some more ways to iterate:

scala>  xs.foreach (println) 
first
second
third

foreach, and similar, map, which would return something (the results of the function, which is, for println, Unit, so a List of Units)

scala> val lens = for (x <- xs) yield (x.length) 
lens: Array[Int] = Array(5, 6, 5)

work with the elements, not the index

scala> ("" /: xs) (_ + _) 
res21: java.lang.String = firstsecondthird

folding

for(int i=0, j=0; i+j<100; i+=j*2, j+=i+2) {...}

can be done with recursion:

def ijIter (i: Int = 0, j: Int = 0, carry: Int = 0) : Int =
  if (i + j >= 100) carry else 
    ijIter (i+2*j, j+i+2, carry / 3 + 2 * i - 4 * j + 10) 

The carry-part is just some example, to do something with i and j. It needn't be an Int.

for simpler stuff, closer to usual for-loops:

scala> (1 until 4)
res43: scala.collection.immutable.Range with scala.collection.immutable.Range.ByOne = Range(1, 2, 3)

scala> (0 to 8 by 2)   
res44: scala.collection.immutable.Range = Range(0, 2, 4, 6, 8)

scala> (26 to 13 by -3)
res45: scala.collection.immutable.Range = Range(26, 23, 20, 17, 14)

or without order:

List (1, 3, 2, 5, 9, 7).foreach (print)