Scala mapping (Map)

concept

Map can be called mapping. It is composed of a collection of keys. In the scala, Map is also divided into variable and immutable Map Map.

Immutable Map

definition

grammar

val/var map = Map(键->值, 键->值, 键->值...)	// 推荐，可读性更好
val/var map = Map((键, 值), (键, 值), (键, 值), (键, 值)...)

The sample code

//定义一个映射，包含学生姓名和年龄数据 zhangsan 18   lisi 20
//方式一
val map = Map("zhangsan"->18, "lisi"->20)
//方式二
val map = Map(("zhangsan", 18), ("lisi", 20))
//获取zhangsan的年龄 根据key获取value
map("zhangsan")

Variable Map

Defines the syntax and the same immutable Map. But the definition need to manually import variable Mapimport scala.collection.mutable.Map

The sample code

//定义一个映射，包含学生姓名和年龄数据  zhangsan 18 lisi 20
//完整写法
val map: mutable.Map[String, Int] = mutable.Map("zhangsan"->18, "lisi"->20)
//省略写法  mutable 不建议省略 这样能更好区分
val map = mutable.Map("zhangsan"->18, "lisi"->20)
//修改 zhangsan 的年龄为 15
 map("zhangsan") = 15
 //输出修改后的值
 println(map)

Basic mapping operation

Basic Operations

• Get the value ( map(key))
• Get all Key map.keys( )
• Get all value map.values( )
• Traversal map collection
• Getorelse
• Increase key, value for
• Delete key

The sample code

//定义一个映射，包含学生姓名和年龄数据  zhangsan 18 lisi 20
 val map = Map("zhangsan"->18, "lisi"->20)
//获取zhangsan的年龄
map("zhangsan")
//获取所有的学生姓名
map.keys
//获取所有的学生年龄
map.values
//打印所有的学生姓名和年龄
for((x,y) <- map) println(s"$x $y")
//获取wangwu的年龄，如果wangwu不存在，则返回-1
map.getOrElse("wangwu", -1)
//新增一个学生：wangwu, 35
 map + "wangwu"->35
//将lisi从可变映射中移除
map - "lisi"
//打印map
println(map)