值连接不是 org.apache.spark.rdd.RDD 的成员

我收到此错误：

value join is not a member of 
    org.apache.spark.rdd.RDD[(Long, (Int, (Long, String, Array[_0])))
        forSome { type _0 <: (String, Double) }]

我发现的唯一建议是import org.apache.spark.SparkContext._我已经在这么做了。

我究竟做错了什么？

编辑：更改代码以消除forSome（即，当对象具有类型org.apache.spark.rdd.RDD[(Long, (Int, (Long, String, Array[(String, Double)])))）解决了问题。 这是 Spark 中的错误吗？

join是的成员org.apache.spark.rdd.PairRDDFunctions。那么为什么隐式类没有触发呢？

scala> val s = Seq[(Long, (Int, (Long, String, Array[_0]))) forSome { type _0 <: (String, Double) }]()
scala> val r = sc.parallelize(s)
scala> r.join(r) // Gives your error message.
scala> val p = new org.apache.spark.rdd.PairRDDFunctions(r)
<console>:25: error: no type parameters for constructor PairRDDFunctions: (self: org.apache.spark.rdd.RDD[(K, V)])(implicit kt: scala.reflect.ClassTag[K], implicit vt: scala.reflect.ClassTag[V], implicit ord: Ordering[K])org.apache.spark.rdd.PairRDDFunctions[K,V] exist so that it can be applied to arguments (org.apache.spark.rdd.RDD[(Long, (Int, (Long, String, Array[_0]))) forSome { type _0 <: (String, Double) }])
 --- because ---
argument expression's type is not compatible with formal parameter type;
 found   : org.apache.spark.rdd.RDD[(Long, (Int, (Long, String, Array[_0]))) forSome { type _0 <: (String, Double) }]
 required: org.apache.spark.rdd.RDD[(?K, ?V)]
Note: (Long, (Int, (Long, String, Array[_0]))) forSome { type _0 <: (String, Double) } >: (?K, ?V), but class RDD is invariant in type T.
You may wish to define T as -T instead. (SLS 4.5)
       val p = new org.apache.spark.rdd.PairRDDFunctions(r)
               ^
<console>:25: error: type mismatch;
 found   : org.apache.spark.rdd.RDD[(Long, (Int, (Long, String, Array[_0]))) forSome { type _0 <: (String, Double) }]
 required: org.apache.spark.rdd.RDD[(K, V)]
       val p = new org.apache.spark.rdd.PairRDDFunctions(r)

我确信其他人都清楚该错误消息，但对于我自己来说，让我们尝试理解它。PairRDDFunctions有两个类型参数，K and V. Your forSome是针对整个对的，因此不能将其分成单独的K and V类型。没有K and V that RDD[(K, V)]等于你的 RDD 类型。

但是，您可以拥有forSome仅适用于密钥，而不适用于整个密钥对。 Join 现在可以工作了，因为这种类型可以分为K and V.

scala> val s2 = Seq[(Long, (Int, (Long, String, Array[_0])) forSome { type _0 <: (String, Double) })]()
scala> val r2 = sc.parallelize(2s)
scala> r2.join(r2)
res0: org.apache.spark.rdd.RDD[(Long, ((Int, (Long, String, Array[_0])) forSome { type _0 <: (String, Double) }, (Int, (Long, String, Array[_0])) forSome { type _0 <: (String, Double) }))] = MapPartitionsRDD[5] at join at <console>:26