Transform this iterative solution to functional solution

Question

This class takes a Map of type [String , List[String]] and outputs a Map of [String, String] where the key is the name of the List and the values is binary representation of the letters. Each digit corresponds to if the letter appears in the List or not. 1 - it appears, 0 - it does not appear. For example this List :

1 = 1,1,0,0
2 = 1,1,1,0
3 = 1,1,0,1
4 = 1,1,0,0

 Returns

4-->1100
1-->1100
2-->1110
3-->1101

Below is an iterative solution :

object BinaryRep {

  var userDetails : scala.collection.immutable.HashMap[String, List[String]] = new  scala.collection.immutable.HashMap[String, List[String]] 
  var lettersToCheck = List("a" , "b" , "c"  ,"d")
  def main(args: Array[String]) {

    userDetails += "1" -> List("a" , "b")
    userDetails += "2" -> List("a" , "b" , "c")
    userDetails += "3" -> List("a" , "b" , "d")
    userDetails += "4" -> List("a" , "b")

    val binRep = getBinaryRepresentation

    getBinaryRepresentation foreach ( (t2) => println (t2._1 + "-->" + t2._2))

  }

  def getBinaryRepresentation = {

    var mapvalues = new scala.collection.immutable.HashMap[String, String]
    var binaryRep = "";

    for (usd <- userDetails) {
      for (letter <- lettersToCheck) {
        if (usd._2.contains(letter)) {
          binaryRep += "1"
        } else {
          binaryRep += "0";
        }
      }
      mapvalues += usd._1 -> binaryRep
      binaryRep = "";
    }
    mapvalues

  }


}

I think this is a quite messy but its the best I could do. What is more functional approach to accomplish same result ?

wingedsubmariner · Accepted Answer · 2013-08-28 21:59:09Z

2

import scala.collection.immutable.HashMap

object BinaryRep {
  val userDetails = HashMap("1" -> "ab",
                            "2" -> "abc",
                            "3" -> "abd",
                            "4" -> "ab")
  val lettersToCheck = "abcd"
  def getBinaryRepresentation = userDetails.mapValues(string => lettersToCheck.map(letter => if (string.contains(letter)) '1' else '0'))

  getBinaryRepresentation foreach ( (t2) => println (t2._1 + "-->" + t2._2))
}

Data transformation like this can almost always be implement as some series of map calls.

answered Aug 28, 2013 at 21:59

wingedsubmariner

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