filter, foreach and map functions in scala

Author: CodeLab20

Special_Functions/FilterFunction.scala

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+/***
+* 1. filter filters out elements that meet predicates criteria
+* 2. filterNot filters out elements that do not meed predicates criteria.
+* 3. exists tests if something exists in a collection based on a function
+* 4. These methods are available on List, Range, Set, Map, String, Option etc.
+***/
+object FilterFunction extends App
+{
+    val a = 1 to 10
+    
+    //filter function
+    println("a.filter(x => x % 2 == 0) : " + a.filter(x => x % 2 == 0))  //Filter even numbers
+    
+    //filterNot function
+    println("a.filterNot(x => x % 2 == 0) : " + a.filterNot(x => x % 2 == 0))  //Filter odd numbers
+
+    //exists
+    println("a.exists(_ % 2 == 0) : " + a.exists(_ % 2 == 0))       //does a contain even numbers
+    
+    //filter function using a string
+    def filterVowels(s:String) = s.toLowerCase().filter(c => Set('a', 'e', 'i', 'o', 'u').contains(c))
+    println("filterVowels(\"Orange\") :" + filterVowels("Orange"))
+
+    //filter function on a set
+    val b = Set("Red", "Green", "Purple", "Blue", "Orange");
+    
+    //filter colours containing no. vowels > 1
+    println("b.filter(s => filterVowels(s).size > 1) : " + b.filter(s => filterVowels(s).size > 1))        
+    
+    //filter function on a map
+    val c = Map(1 -> "One", 2 -> "Two", 3 -> "Three", 4 -> "Four")
+    println("c.filterKeys( _ % 2 == 0) : " + c.filterKeys( _ % 2 == 0))      //filter even keys
+    
+    //filter function on Option
+    println("Some(5).filter(_ % 2 == 0) : " + Some(5).filter(_ % 2 == 0))
+    println("Some(4).filter(_ % 2 == 0) : " + Some(4).filter(_ % 2 == 0))
+    
+}
+
+/**
+    Sample Output
+a.filter(x => x % 2 == 0) : Vector(2, 4, 6, 8, 10)
+a.filterNot(x => x % 2 == 0) : Vector(1, 3, 5, 7, 9)
+a.exists(_ % 2 == 0) : true
+filterVowels("Orange") :oae
+b.filter(s => filterVowels(s).size > 1) : Set(Blue, Green, Purple, Orange)
+c.filterKeys( _ % 2 == 0) : Map(2 -> Two, 4 -> Four)
+Some(5).filter(_ % 2 == 0) : None
+Some(4).filter(_ % 2 == 0) : Some(4)
+**/

Special_Functions/ForEachFunction.scala

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+/**
+    1. foreach is a method that takes a function which takes each element and returns unit
+    2. Useful if you want to print to screen
+    3. foreach available on List, Range, Set, Map, String, Option, Streams etc.
+    4. Difference between map and foreach is map must return something
+**/
+object ForEachFunction extends App
+{
+    val a = 1 to 10
+    a.foreach( x => println(x))
+    
+    //above line can be reduced to
+/*    a foreach(  println _)
+    a foreach println
+*/
+}
+
+/**
+    Sample Output
+1  
+2  
+3  
+4  
+5  
+6  
+7  
+8  
+9  
+10 
+**/

Special_Functions/MapFunction.scala

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+object MapFunction extends App
+{
+    //Applying map function on a list
+    val a = List(1,2,3,4,5,6)
+    val f = (x:Int)=> x+1
+    
+    println("a.map(f) :" + a.map(f))
+    println("a.map((x:Int) => x+1) : " + a.map((x:Int) => x+1))
+    println("a.map(x => x+1):" + a.map(x => x+1))
+    println("a.map(_ + 1):" + a.map(_ + 1))
+    println("a.map(1 + _):" + a.map(1 + _))
+    
+    //This import is required to remove compilation warning as-
+    //warning: there was one feature warning; re-run with -feature for details
+    import scala.language.postfixOps        
+    println("a.map(1+):" + a.map(1+))   //since we have removed _ for 1+ above warning is displayed
+    
+    //Applying map function on a Set
+    var b = Set("Brown", "Red", "Green", "Purple", "Grey", "Yellow")
+    println("b.map(x => x.size):" + b.map(x => x.size))     //Remember, Set contains unique values only.
+    println("b.map(_.size):" + b.map(_.size))
+    println("b.map(x => (x, x.size)): " + b.map(x => (x, x.size)))
+    
+    //Applying map function on a Map 
+    val fifaTeams = Map('Germany -> 4, 'Brazil -> 5 , 'Italy -> 4, 'Argentina -> 2 )
+    println("fifaTeams.map(t => (Symbol.apply(\"Team \" + t._1.name), t._2)) : " + fifaTeams.map(t => (Symbol.apply("Team " + t._1.name), t._2)))
+    
+    //Applying map function on a String
+    println("\"Hello!\".map(x => (x+1)).toChar:" + "Hello!".map(x => (x+1).toChar))
+    
+    //Applying map function on Some
+    println("Some(4).map(1+) :" + Some(4).map(1+))
+    
+    //Applying map function on None
+    println("None.asInstanceOf[Option[Int]].map(1+) :" + None.asInstanceOf[Option[Int]].map(1+))
+}
+
+/**
+    Sample Output
+a.map(f) :List(2, 3, 4, 5, 6, 7)
+a.map((x:Int) => x+1) : List(2, 3, 4, 5, 6, 7)
+a.map(x => x+1):List(2, 3, 4, 5, 6, 7)
+a.map(_ + 1):List(2, 3, 4, 5, 6, 7)
+a.map(1 + _):List(2, 3, 4, 5, 6, 7)
+a.map(1+):List(2, 3, 4, 5, 6, 7)
+b.map(x => x.size):Set(6, 3, 5, 4)
+b.map(_.size):Set(6, 3, 5, 4)
+b.map(x => (x, x.size)): Set((Green,5), (Brown,5), (Red,3), (Yellow,6), (Grey,4), (Purple,6))
+fifaTeams.map(t => (Symbol.apply("Team " + t._1.name), t._2)) : Map('Team Germany -> 4, 'Team Brazil -> 5, 'Team Italy -> 4, 'Team Argentina -> 2)
+"Hello!".map(x => (x+1)).toChar:Ifmmp"
+Some(4).map(1+) :Some(5)
+None.asInstanceOf[Option[Int]].map(1+) :None    
+
+**/