Function to check elements in an array in scala

Question

def f(c: String) = {
  val array = ("google.com|yahoo.com|gmail.com|mail.com").split("\\|")
  for (i <- array) {
    if (c.contains(i)) {
      println("comparing " + c + " with " + i)
      i
    }
  }
  "N/A"
}

My intention for the above function is that, it will return N/A if c does not contain any of the elements of the array. And, if it does, it will return the element in the array. So if c="www.google.com/1234" , ideally the function would return google.com and if c="bloomberg.com/example", the function will return N/A.

But when I do println(f("www.google.com/1234")) I get N/A. Can anyone tell me what am I doing wrong.

The for() statement goes through the entire array. After it's finished the program moves to the next line: "N/A" Since that's the last line of the method, that's what the method returns, no matter what happens in the for().. — jwvh
– jwvh, Commented Mar 20, 2018 at 0:35

laughedelic · Accepted Answer · 2018-03-20 02:26:50Z

2

Your function always returns N/A, because it's the last value in its definition. To leave a value in the end like this means in Scala the same as writing return "N/A". But even without N/A in the end, your function wouldn't return what you want, because:

the last statement would be for { ... } which is of type Unit
your function is side-effecting, by calling println, it's not the same as returning a value

Let's write first a function that tries to find a match:

def findMatch(c: String): Option[String] = {
  val array = "google.com|yahoo.com|gmail.com|mail.com".split('|')
  array.find(c.contains)
}

Notice that the return type is Option[String] which comes from the call to the find method. Now you can use it to print the result if it's there or N/A otherwise:

def f(c: String): Unit = {
  println(findMatch(c).getOrElse("N/A"))
}

answered Mar 20, 2018 at 2:26

laughedelic

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user unknown · Accepted Answer · 2018-03-20 12:10:39Z

While laughedelics solution looks fine, another one, on your track, is possible too:

def f (c: String) : List[String] = {
  val array = ("google.com|yahoo.com|gmail.com|mail.com").split("\\|")
  val list = (for (i <- array 
    if (c.contains(i))) yield {
      println("comparing " + c + " with " + i)
      i
    }).toList
  if (list.isEmpty) List ("N/A") else list
}

It prints while iterating and either returns a list of matches, or a List with the String "N/A", which should, in practice, in most cases result in a List of exactly one String, not less or more, but depending on the input, more than one match is possible.

scala> f ("www.google.com/1234")
comparing www.google.com/1234 with google.com
res61: List[String] = List(google.com)

scala> f ("www.göögle.com/1234")
res62: List[String] = List(N/A)

scala> f ("www.google.com/1234?param:subject='mail.com'")
comparing www.google.com/1234?param:subject='mail.com' with google.com
comparing www.google.com/1234?param:subject='mail.com' with mail.com
res63: List[String] = List(google.com, mail.com)

The main difference to your approach is the use of a yield, to return something from the for-construct.

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