Scala：如何将模式匹配功能应用于包含以下提到的值的csv文件

Question

def matchcase(x:String):Int =  x match{
        case "Iris-setosa" => 10
        case "Iris-virginica" => 20
        case "Iris-versicolor"=> 30
        case _ => 0

csv文件中的示例数据如下：

1,5.1,3.5,1.4,0.2,Iris-setosa
2,4.9,3,1.4,0.2,Iris-setosa
3,4.7,3.2,1.3,0.2,Iris-setosa
51,7,3.2,4.7,1.4,Iris-versicolor
52,6.4,3.2,4.5,1.5,Iris-versicolor
53,6.9,3.1,4.9,1.5,Iris-versicolor
103,7.1,3,5.9,2.1,Iris-virginica
104,6.3,2.9,5.6,1.8,Iris-virginica
105,6.5,3,5.8,2.2,Iris-virginica

Answer 1

在带有正则表达式的Scala中使用提取器模式

鉴于正则表达式

val regex = "[[0-9]|,|\\.]+([[a-zA-z]|\\-]+)".r

现在Just模式逐行匹配整个文本

lines.map {
  case regex(name) => Some(name)
  case _ => None
}

稍后使用matchCase函数将字符串（名称）转换为数字并将名称替换为数字

为您寻找的代码

lines.map { line =>
  line match {
   case regex(name) => line.replace("[[a-zA-z]|\\-]+", matchcase(name).toString)
   case _ => line
  }
}

斯卡拉REPL

scala> val regex = "[[0-9]|,|\\.]+([[a-zA-z]|\\-]+)".r
regex: scala.util.matching.Regex = [[0-9]|,|\.]+([[a-zA-z]|\-]+)

scala> "1,5.1,3.5,1.4,0.2,Iris-setosa" match { case regex(str) => println(s"name: $str")}
name: Iris-setosa

下一个

处理全文

scala> val text = """
     | 1,5.1,3.5,1.4,0.2,Iris-setosa
     | 2,4.9,3,1.4,0.2,Iris-setosa
     | 3,4.7,3.2,1.3,0.2,Iris-setosa
     | 51,7,3.2,4.7,1.4,Iris-versicolor
     | 52,6.4,3.2,4.5,1.5,Iris-versicolor
     | 53,6.9,3.1,4.9,1.5,Iris-versicolor
     | 103,7.1,3,5.9,2.1,Iris-virginica
     | 104,6.3,2.9,5.6,1.8,Iris-virginica
     | 105,6.5,3,5.8,2.2,Iris-virginica
     | """.stripMargin
text: String =
"
1,5.1,3.5,1.4,0.2,Iris-setosa
2,4.9,3,1.4,0.2,Iris-setosa
3,4.7,3.2,1.3,0.2,Iris-setosa
51,7,3.2,4.7,1.4,Iris-versicolor
52,6.4,3.2,4.5,1.5,Iris-versicolor
53,6.9,3.1,4.9,1.5,Iris-versicolor
103,7.1,3,5.9,2.1,Iris-virginica
104,6.3,2.9,5.6,1.8,Iris-virginica
105,6.5,3,5.8,2.2,Iris-virginica
"

scala> val lines = text.split("\n").filter(_.trim.nonEmpty)
lines: Array[String] = Array(1,5.1,3.5,1.4,0.2,Iris-setosa, 2,4.9,3,1.4,0.2,Iris-setosa, 3,4.7,3.2,1.3,0.2,Iris-setosa, 51,7,3.2,4.7,1.4,Iris-versicolor, 52,6.4,3.2,4.5,1.5,Iris-versicolor, 53,6.9,3.1,4.9,1.5,Iris-versicolor, 103,7.1,3,5.9,2.1,Iris-virginica, 104,6.3,2.9,5.6,1.8,Iris-virginica, 105,6.5,3,5.8,2.2,Iris-virginica)

scala> lines.map {
     |  case regex(name) => Some(name)
     |  case _ => None
     | }
res18: Array[Option[String]] = Array(Some(Iris-setosa), Some(Iris-setosa), Some(Iris-setosa), Some(Iris-versicolor), Some(Iris-versicolor), Some(Iris-versicolor), Some(Iris-virginica), Some(Iris-virginica), Some(Iris-virginica))

现在使用collect并且只收集Some值

scala> res18.collect { case Some(value) => value }
res19: Array[String] = Array(Iris-setosa, Iris-setosa, Iris-setosa, Iris-versicolor, Iris-versicolor, Iris-versicolor, Iris-virginica, Iris-virginica, Iris-virginica)

scala> res19.mkString("\n")
res20: String =
Iris-setosa
Iris-setosa
Iris-setosa
Iris-versicolor
Iris-versicolor
Iris-versicolor
Iris-virginica
Iris-virginica
Iris-virginica

Answer 2

在您的评论中您提到了

实际上我想通过使用matchcase函数替换整个文件中的文本

并假设您具有问题中提到的数据和功能，则可以使用scala.io.Source.fromFile读取文件

val data = scala.io.Source.fromFile("input file path")

调用您编写的matchcase函数

val replacedData = data.getLines().map(_.split(",")).map(array => array.init.mkString(",")+","+matchcase(array.last))

最后写输出

new PrintWriter("path to output file"){write(replacedData.mkString("\n")); close}

您应该有一个包含以下数据的文件

1,5.1,3.5,1.4,0.2,10
2,4.9,3,1.4,0.2,10
3,4.7,3.2,1.3,0.2,10
51,7,3.2,4.7,1.4,30
52,6.4,3.2,4.5,1.5,30
53,6.9,3.1,4.9,1.5,30
103,7.1,3,5.9,2.1,20
104,6.3,2.9,5.6,1.8,20
105,6.5,3,5.8,2.2,20

我希望答案是有帮助的