如何更新 dataframe Spark Scala 的单元格中的值

Question

我正在尝试在 reddit May2015 数据集上实现 pagerank 算法，但我无法提取评论中引用的 subreddits。 一列包含 subreddit 的名称，另一列包含发布在该 subreddit 中的评论，该评论引用了另一个 subreddit。

   subreddit                body

      videos|"Tagged you as ""...
      Quebec|Ok, c'est quoi le...
     pokemon|Sorry to hear abo...
      videos|Not sure what the...
ClashOfClans|Your submission, ...
    realtech|Original /r/techn...
        guns|Welp, those basta...
        IAmA|If you are very i...
         WTF|If you go on /r/w...
     Fitness|Your submission h...
        gifs|Hi! Take a look a...
   Coachella|Yeah. If you go /...

我所做的是这样的：

val df = spark.read
      .format("csv")
      .option("header", "true")
      .load("path\\May2015.csv")

val df1 = df.filter(df("body").contains("/r/")).select("subreddit", "body")

val lines = df1.rdd

val links = lines.map{ s =>
      val x = s(1).toString.split(" ")
        val b = x.filter(_.startsWith("/r/")).toList
        val t = b(0)
        (s(0), t)
    }.distinct().groupByKey().cache()
 var ranks = links.mapValues(v =>0.25)
 for (i <- 1 to iters) {
      val contribs = links.join(ranks).values.flatMap{ case (urls, rank) =>
      val size = urls.size
      urls.map(url =(url, rank / size))
      }
     ranks = contribs.reduceByKey(_ + _).mapValues(0.15 + 0.85 * _)
    }

问题是 output 总是：

(subreddit, CompactBuffer())

虽然我想要的是：

(subreddit, anothersubreddit)

我设法解决了这个问题，但现在我遇到了另一个错误：

> type mismatch;  found   : org.apache.spark.rdd.RDD[(String, Double)] 
> required: org.apache.spark.rdd.RDD[(Any, Double)] Note: (String,
> Double) <: (Any, Double), but class RDD is invariant in type T. You
> may wish to define T as +T instead. (SLS 4.5)
>       ranks = contribs.reduceByKey(_ + _).mapValues(0.15 + 0.85 * _)

Answer 1

问题大概出在这里

val links = lines.map{ s =>
  val x = s(1).toString.split(" ")
  val b = x.filter(_.startsWith("/r/")).toList
  val t = b(0)
  (s(0), t)
...

您需要在此处避免元组的第一个元素为Any ，因此如果您希望s(0)可能具有String类型，您可以使用显式转换，如s(0).asInstanceOf[String]或通过方法s.getAs[String]甚至s.getString(0) 。

所以，解决编译错误的版本可能如下：

val links = lines.map{ s =>
  val x = s.getString(1).split(" ")
  val b = x.filter(_.startsWith("/r/")).toList
  val t = b(0)
  (s.getString(0), t)
...