scala中map添加值
A Map is a data structure that stores data as key: value pair.
映射是一种将数据存储为键：值对的数据结构。
Syntax:
句法：
Map(key->value, key->value)
反转地图中的键和值 (Reversing Keys and values in Map)
Here, we will see a program to reverse keys and values in Scala Map. We will reverse the values to keys and the keys to pairs.
在这里，我们将看到一个在Scala Map中反转键和值的程序 。 我们将值反转为键，将键反转为对。
So, before this, we will have to make sure that both keys and values of the initial map are unique to avoid errors.
因此，在此之前，我们必须确保初始映射的键和值都唯一以避免错误。
Program:
程序：
object myObject {
def main(args:Array[String]) {
val bikes = Map(1->"S1000RR" , 2->"R1", 3->"F4" )
println("Inital map: " + bikes)
val reverse = for ((a, b) <- bikes) yield (b, a)
println("Reversed map: " + reverse)
}
}
Output
输出量
Inital map: Map(1 -> S1000RR, 2 -> R1, 3 -> F4)
Reversed map: Map(S1000RR -> 1, R1 -> 2, F4 -> 3)
Explanation:
说明：
Here, we have declared a map and then reversed its values. In the reverse variable, we have inserted value that is reverse of each pair of the original map, the yield methods take the (key, value) pair and returns (value, key) pair to the reverse map.
在这里，我们声明了一个映射，然后反转了它的值。 在反向变量中，我们插入了与原始映射的每对相反的值，yield方法采用( key，value )对，然后将( value，key )对返回到反向映射。
What if values are not unique?
如果值不是唯一的怎么办？
There is a thing that is needed to be considered is both key-value pairs should be unique. But if we insert a duplicate in value, in the reverse map this will delete that pair.
有一点需要考虑的是，两个键值对都应该是唯一的。 但是，如果我们在值中插入重复项，则在反向映射中将删除该对。
Program:
程序：
object myObject {
def main(args:Array[String]) {
val bikes = Map(1->"S1000RR" , 2->"R1", 3->"F4", 4->"S1000RR" )
println("Inital map: " + bikes)
val reverse = for ((a, b) <- bikes) yield (b, a)
println("Reversed map: " + reverse)
}
}
Output
输出量
Inital map: Map(1 -> S1000RR, 2 -> R1, 3 -> F4, 4 -> S1000RR)
Reversed map: Map(S1000RR -> 4, R1 -> 2, F4 -> 3)
So, the code runs properly but the reverse will delete the pair 4->S100RR to make all the keys of reverse map unique.
因此，代码可以正常运行，但是反向键将删除对4-> S100RR以使反向键的所有键都唯一。
翻译自: https://www.includehelp.com/scala/reverse-keys-and-values-in-scala-map.aspx
scala中map添加值
