[scala] range와 함수 내용을 넣은 Map 만들기- 예제

1부터 28까지의 숫자를 특정 함수에 넣고 그 값을 Map으로 리턴하고 싶다고 한다면. 다음과 같을 것이다. 

scala> def multiply(num: Int): Int = { num *2 }

multiply: (num: Int)Int

scala> (1 to 28).map { i => (i, multiply(i)) }.toMap

res23: scala.collection.immutable.Map[Int,Int] = Map(5 -> 10, 10 -> 20, 24 -> 48, 25 -> 50, 14 -> 28, 20 -> 40, 1 -> 2, 6 -> 12, 28 -> 56, 21 -> 42, 9 -> 18, 13 -> 26, 2 -> 4, 17 -> 34, 22 -> 44, 27 -> 54, 12 -> 24, 7 -> 14, 3 -> 6, 18 -> 36, 16 -> 32, 11 -> 22, 26 -> 52, 23 -> 46, 8 -> 16, 19 -> 38, 4 -> 8, 15 -> 30)

키로 정렬하려면 TreeMap을 활용하면 깔끔히 정렬된다.

scala> val sortedMap = scala.collection.immutable.TreeMap(map.toSeq:_*)

sortedMap: scala.collection.immutable.TreeMap[Int,Int] = Map(1 -> 2, 2 -> 4, 3 -> 6, 4 -> 8, 5 -> 10, 6 -> 12, 7 -> 14, 8 -> 16, 9 -> 18, 10 -> 20, 11 -> 22, 12 -> 24, 13 -> 26, 14 -> 28, 15 -> 30, 16 -> 32, 17 -> 34, 18 -> 36, 19 -> 38, 20 -> 40, 21 -> 42, 22 -> 44, 23 -> 46, 24 -> 48, 25 -> 50, 26 -> 52, 27 -> 54, 28 -> 56)

예쁘게 출력하려면 mkString을 사용한다. 

scala> sortedMap.mkString("\n")

res28: String =

1 -> 2

2 -> 4

3 -> 6

4 -> 8

5 -> 10

6 -> 12

7 -> 14

8 -> 16

9 -> 18

10 -> 20

11 -> 22

12 -> 24

13 -> 26

14 -> 28

15 -> 30

16 -> 32

17 -> 34

18 -> 36

19 -> 38

20 -> 40

21 -> 42

22 -> 44

23 -> 46

24 -> 48

25 -> 50

26 -> 52

27 -> 54

28 -> 56

참고로 주의할 점은 (1 to 28) 과 Collection(1 to 28)은 다르다..

scala> (1 to 28)

res24: scala.collection.immutable.Range.Inclusive = Range(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28)

scala> List(1 to 28)

res25: List[scala.collection.immutable.Range.Inclusive] = List(Range(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28))