scala - 错误: value saveAsTextFile is not a member of Unit

Question

我是Spark和Scala编程的新手。

我试图使用Scala执行简单的pagerank算法。但是我在编译时遇到了这个错误。

error: value saveAsTextFile is not a member of Unit

我已经附上了我正在使用的代码。

val output = ranks.collect()
output.foreach(tup => println(tup._1 + " has page rank: " + tup._2)).saveAsTextFile("/user/ssimhadr/ScalaWordCount_Output")

Answer 1

正如Ryan所指出的，foreach仅用于副作用。它返回Unit而不是List本身。 Ergo没有链接。

现在，您实际正在执行以下操作:

val output = ranks.collect()
val realoutput: Unit = output.foreach(tup => println(tup._1 + " has page rank: " + tup._2))
realoutput.saveAsTextFile(...)

saveAsTextFile不是 Unit的成员，您会收到错误消息

您应该这样做:

ranks.foreach(tup => println(tup._1 + " has page rank: " + tup._2))
ranks.saveAsTextFile(...)

要么

ranks.saveAsTextFile(...)
ranks.collect().foreach(tup => println(tup._1 + " has page rank: " + tup._2))