Count number of Strings that can be converted to Int in a List

Question

For example, my input is:

scala> val myList = List("7842", "abf45", "abd", "56")
myList: List[String] = List(7842, abf45, abd, 56)

7842 and 56 can be converted to Int; therefore, my expected output is 2. We can assume that negative integers don't happen, so -67 is not possible.

This is what I have so far:

scala> myList.map(x => Try(x.toInt).getOrElse(-1)).count(_ > -1)
res15: Int = 2

This should work correctly, but I feel like I am missing a more elegant and readable solution, because all I have to do is count number of successes.

Answer 1

I would caution against using exception handling (like Try) in control flow -- it's very slow.

Here's a solution that uses idiomatic Scala collection operations, performs well, and will not count negative numbers:

scala> val myList = List("7842", "abf45", "abd", "56")
myList: List[String] = List(7842, abf45, abd, 56)

scala> myList.count(_.forall(_.isDigit)) 
res8: Int = 2

EDIT: @immibis pointed out that this won't detect strings of numbers that exceed Integer.MaxValue. If this is a concern, I would recommend one of the following approaches:

import scala.util.Try
myList.count(x => Try(x.toInt).filter(_ >= 0).isSuccess)

or, if you want to keep the performance of my first answer while still handling this edge case:

import scala.util.Try
myList.count(x => x.forall(_.isDigit) && Try(x.toInt).filter(_ >= 0).isSuccess)

Answer 2

This is a bit shorter:

myList.count(x => Try(x.toInt).isSuccess)

Note that this solution will handle any string that can be converted to integer via .toInt, including negative numbers.