Bubble Foundry

Comparing Software Version Numbers

by Peter.

Software version numbers tend to be in the format ‘Major.minor.point’, which makes sorting versions require a little bit of work. If we only had a single dot we could just convert them to numbers and use < and >. However, we often don’t and sometimes people put letters in their versions also, like ‘1.2.A’.

Here’s my solution, in Scala:

def compAsc(a: String, b: String): Boolean = {
  val separator = '.'
  val aSplit = List.fromString(a, separator)
  val bSplit = List.fromString(b, separator)
 
  def comp(a: List[String], b: List[String]): Boolean = {
    !a.isEmpty match {
      case true if !b.isEmpty => {
        if (a.head == b.head) {
          // if both equal, keep comparing
          comp(a.tail, b.tail)
        }
        else {
          a.head < b.head
        }
      }
      // if a has a value but b doesn't then a is larger
      case true if b.isEmpty => false
      // if a doesn't have a value but b does then b is larger
      case false if !b.isEmpty => true
      // in all other cases assume a is larger
      case _ => true
    }
  }
 
  comp(aSplit, bSplit)
}
 
def compDesc(a: String, b: String): Boolean = {
  val separator = '.'
  val aSplit = List.fromString(a, separator)
  val bSplit = List.fromString(b, separator)
 
  def comp(a: List[String], b: List[String]): Boolean = {
    !a.isEmpty match {
      case true if !b.isEmpty => {
        if (a.head == b.head) {
          // if both equal, keep comparing
          comp(a.tail, b.tail)
        }
        else {
          a.head > b.head
        }
      }
      // if a has a value but b doesn't then a is larger
      case true if b.isEmpty => true
      // if a doesn't have a value but b does then b is larger
      case false if !b.isEmpty => false
      // in all other cases assume a is larger
      case _ => false
    }
  }
 
  comp(aSplit, bSplit)
}

Some examples:

scala> val l = List("1.24", "3.2", "3.0", "3.0.1 beta")
l: List[java.lang.String] = List(1.24, 3.2, 3.0, 3.0.1 beta)
 
scala> l.sort(compAsc)
res0: List[java.lang.String] = List(1.24, 3.0, 3.0.1 beta, 3.2)
 
scala> l.sort(compDesc)
res1: List[java.lang.String] = List(3.2, 3.0.1 beta, 3.0, 1.24)

And why, do you ask, am I working with software version numbers? Let’s just say it has something to do with www.mobtest.com. More soon!