英文:
Making a Graph in Spark GraphX using Java bindings: What are those "evidence" arguments?
问题
在Spark GraphX javadoc中，fromEdges()方法具有未记录的参数，如evidence$17。这些很可能是Scala实现的遗留物，但在Java中我应该怎么处理它们？
public static <VD, ED> Graph<VD, ED> fromEdges(RDD<Edge<ED>> edges,
VD defaultValue,
StorageLevel edgeStorageLevel,
StorageLevel vertexStorageLevel,
scala.reflect.ClassTag<VD> evidence$16,
scala.reflect.ClassTag<ED> evidence$17)
更新：我找到了一些其他的Scala/Java示例，似乎正确的做法是ClassTag$.MODULE$.apply(myClass)，其中myClass分别是VD或ED类型的类。尽管这实际上并不起作用，因为它会导致后来出现神秘的异常，比如在org.apache.spark.graphx.impl.EdgePartitionBuilder.toEdgePartition中出现java.lang.ArrayStoreException: java.lang.Integer的异常。
更新：确实，ClassTag$.MODULE$.apply(Long.class)对我有效。我之前遇到的错误是因为我将默认值设置为1而不是1L。
英文:
In the Spark GraphX javadoc the fromEdges() method has undocumented arguments like evidence$17. Presumably these are artifacts of the Scala implementation, but what should I do with them in Java?
public static <VD,ED> Graph<VD,ED> fromEdges(RDD<Edge<ED>> edges,
VD defaultValue,
StorageLevel edgeStorageLevel,
StorageLevel vertexStorageLevel,
scala.reflect.ClassTag<VD> evidence$16,
scala.reflect.ClassTag<ED> evidence$17)
UPDATE: found some other Scala/Java examples, and it seems like the right thing is ClassTag$.MODULE$.apply(myClass) where myClass is the class of the VD or ED type, respectively. Not that this actually works, as it leads to later, mysterious exceptions, like java.lang.ArrayStoreException: java.lang.Integer deep in org.apache.spark.graphx.impl.EdgePartitionBuilder.toEdgePartition
UPDATE: Indeed, the ClassTag$.MODULE$.apply(Long.class) works for me. The error I was getting was due to passing in 1 for the default value instead of 1L.
答案1
得分: 0
证据参数使用ClassTag$.MODULE$.apply(myClass)填充，其中myClass分别是VD或ED类型的类。
如果您将Long.class用于ED和VD类型，请确保在调用Graph.fromEdges()时使用匹配的默认值。特别是对于Long.class，请使用1L作为默认值，而不是1。
英文:
The evidence arguments are filled in using ClassTag$.MODULE$.apply(myClass) where myClass is the class of the VD or ED type, respectively.
If you use Long.class for the ED and VD types, make sure to use a matching value for the defaults when you call Graph.fromEdges(). In particular for Long.class use e.g. 1L for the default value instead of 1.
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