Scala groupBy 用于列表
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时间：2020-10-22 09:30:11 来源:igfitidea点击:
Scala groupBy for a list
提问by T.Simmari
I'd like to create a map on which the key is the string and the value is the number of how many times the string appears on the list. I tried the groupBymethod, but have been unsuccessful with that.
我想创建一个映射，其键是字符串，值是字符串在列表中出现的次数。我尝试了该groupBy方法，但没有成功。
回答by Mahesh Chand
Required Answer
必填答案
scala> val l = List("abc","abc","cbe","cab")
l: List[String] = List(abc, abc, cbe, cab)
scala> l.groupBy(identity).mapValues(_.size)
res91: scala.collection.immutable.Map[String,Int] = Map(cab -> 1, abc -> 2, cbe -> 1)
回答by Ramesh Maharjan
Suppose you have a listas
假设你有一个清单作为
scala> val list = List("abc", "abc", "bc", "b", "abc")
list: List[String] = List(abc, abc, bc, b, abc)
You can write a function
你可以写一个函数
scala> def generateMap(list: List[String], map:Map[String, Int]) : Map[String, Int] = list match {
| case x :: y => if(map.keySet.contains(x)) generateMap(y, map ++ Map(x -> (map(x)+1))) else generateMap(y, map ++ Map(x -> 1))
| case Nil => map
| }
generateMap: (list: List[String], map: Map[String,Int])Map[String,Int]
Then call the functionas
然后将函数调用为
scala> generateMap(list, Map.empty)
res1: Map[String,Int] = Map(abc -> 3, bc -> 1, b -> 1)
