Scala Stream/Iterator that Generates Excel Column Names? - scala

Question

I would like a Scala Stream/Iterator that generates Excel column names.
e.g. the first would be 'A' second would be 'B' and onwards to 'AA' and beyond.
I have a function (shown below) that does it from an index but it seems wasteful to generate from an index each time when all I'll ever be doing is generating them in order. In practice this isn't a problem so I am fine using this method but just thought I would ask to see if anyone has anything nicer.
val charArray = ('A' to 'Z').toArray
def indexToExcelColumnName(i:Int):String = {
if (i < 0) {
""
} else {
indexToExcelColumnName((i / 26) - 1) + charArray(i % 26)
}
}

Answer 1

Something like that?
class ExcelColumnIterator extends Iterator[String]{
private var currentColumnName = "A"
private def nextColumn(str: String):String = str.last match {
case 'Z' if str.length == 1 => "AA"
case 'Z' => nextColumn(str.init) + 'A'
case c => str.init + (c+1).toChar
}
override def hasNext = true
override def next() = {
val t = currentColumnName
currentColumnName = nextColumn(currentColumnName)
t
}
}

Answer 2

First I'd write something generating names of a fixed size.
val namesOfLength: Int => Iterator[String] = {
case 1 => ('A' to 'Z').iterator.map(_.toString)
case n => ('A' to 'Z').iterator.flatMap(a => namesOfLength(n-1).map(a + _))
}
or
def namesOfLength(n: Int) =
(1 until n).foldLeft[Iterable[String]](('A' to 'Z').view.map(_.toString)) {
case (it, _) => ('A' to 'Z').view.flatMap(a => it.map(a + _))
}
Then chain them together.
Iterator.iterate(1)(_ + 1).flatMap(namesOfLength).take(100).toStream.force

Answer 3

Here's a one-liner solution:
Stream.iterate(List(""))(_.flatMap(s => ('A' to 'Z').map(s + _)))
.flatten.tail
If you'd prefer to get an Iterator out, substitute Iterator.iterate for Stream.iterate and drop(1) for tail.
And here's an alternate solution you might find amusing:
Stream.from(0)
.map(n => Integer.toString(n, 36))
.map(_.toUpperCase)
.filterNot(_.exists(_.isDigit))
😜