How to do a foldLeft with a Map in Scala, plus basic stuff.

MapBasic.scala

val list = (1 to 10).toList

// imutable map
val map1 = list.foldLeft(Map.empty[Int,String])( (map, value) => map + (value -> value.toString) )

// this is equivalent to
val map1 = list.foldLeft(Map.empty[Int,String])( (map, value) => map + ((value, value.toString)) )


// imutable map with more complex value (note the extra parenthesis)
val map2 = list.foldLeft(Map.empty[Int,String])( (map, value) => map + (value -> ("number:" + value.toString)) )

// mutable Map
val map3 = list.foldLeft(scala.collection.mutable.Map.empty[Int,String])( (map, value) => map += (value -> value.toString) )

// Basic Map operations
val map4 = Map[Int,Int]() // immutable map
val map41 = map4 + (1 -> 1) // creates a new Map with (1,"1") as key-value pair
val map42 = map4 + ((2,2), (3,3))
val map43 = map4 + (2->2, 3->3)

val map5 = scala.collection.mutable.Map[Int,Int]() // mutable Map
map5 += 2 -> 2
map5 += ((2,2)) // same as above
map5 += ((1,1), (2,2)) 
map5 += (1->1, 2->2)

map5 + ((8,8)) // creates a NEW MAP with KV (8,8), EVEN THOUGH map5 is mutable
map5 =- 2 // removes key 2
map5 - 2 // creates a NEW MAP without key 2