Scala(四) —— 集合

一、List

var x = List(1,2,3,4)
//x:List[Int] = List(1, 2, 3, 4)

var y = List("x","y","z")
//y: List[String] = List(x, y, z)

0 :: x
//res6: List[Int] = List(0, 1, 2, 3, 4)

x ::: y
//List[Any] = List(1, 2, 3, 4, x, y, z)

scala> "x"::"y"::"z"::Nil
res9: List[String] = List(x, y, z)

x.head //获取第一个元素

x.tail //获取除第一个元素的其他元素

x.isEmpty //判断该列表是否为空

字符串转List

var a = "HelloWorld,2018"
//a: String = HelloWorld,2018

a.toList
//res0: List[Char] = List(H, e, l, l, o, W, o, r, l, d, ,, 2, 0, 1, 8)

filter函数

a.toList.filter(x => Character.isDigit(x))
res1: List[Char] = List(2, 0, 1, 8)

//另一种简写方式

a.toList.filter(_.Character.isDigit(x))

takeWhile函数

a.toList.takeWhile(x => x!='d')
res2: List[Char] = List(H, e, l, l, o, W, o, r, l)

map函数

var a = List(1,2,3,4)

a.map(x => x % 2 == 0)
a.map(_%2 == 0)

var b = List(6,7,8)

var p = List(a,b)

a.map(_.filter(_%2 == 0))
//res14: List[List[Int]] = List(List(2, 4), List(8))

flatMap

a.flatMap(_.filter(_%2 == 0))
//res15: List[Int] = List(2, 4, 8)

reduce函数

a.reduce((x,y) => x+y) 

//等价于

a.reduce(_+_)

foldLeft函数

a.fold(0)((x,y) => x+y) 

//等价于

a.fold(0)(_+_)

二、Tuple元组

元组相当于数据库中的记录，可以放各种不同类型的值

val a = (1,2,3,4)

a._1 //访问元组中第一个元素

a._2 //访问元组中第二个元素

val b = (1,"fzj","math",95)

例子1：返回一条记录，计算一个列表的元素个数、元素之和，元素的平方和

val a = (1,2,3,4)

def sum(list:List[Int]):(Int,Int,Int)={
    list.foldLeft(0,0,0)((x,y) => (x._1 + 1,x._2 + y,x._3 + y*y))
}

三、Set

var x = Set(1,2,3,4)

四、Map

(1) 创建Map

var  x = Map("one" -> "1","two" -> "2")

var x:Map[String,String] = Map()

(2) 添加key-value

x += ("three" -> "three")

(3) 合并

使用 ++运算符 或 Map.++()方法来连接两个Map

var colors = color1 ++ color2

var colors = color1.++(color2)

(4) 遍历

val sites = Map("one"->"one","two"->"two","three"->"three")

sites.keys.foreach{
    i =>
    println("key="+i+",value="+sites(i))
}