Here is another solution (minGraph is the graph from your code. I assume that
is your original graph):
val graphWithNoOutEdges = minGraph.filter(
graph => graph.outerJoinVertices(graph.outDegrees) {(vId, vData,
outDegreesOpt) => outDegreesOpt.getOrElse(0)},
vpred = (vId: VertexId, vOutDegrees: Int) => vOutDegrees == 0
)
val verticesWithNoOutEdges = graphWithNoOutEdges.vertices
Mohammed
Author: Big Data Analytics with
Spark<http://www.amazon.com/Big-Data-Analytics-Spark-Practitioners/dp/1484209656/>
From: Guillermo Ortiz [mailto:[email protected]]
Sent: Friday, February 26, 2016 5:46 AM
To: Robin East
Cc: user
Subject: Re: Get all vertexes with outDegree equals to 0 with GraphX
Yes, I am not really happy with that "collect".
I was taking a look to use subgraph method and others options and didn't figure
out anything easy or direct..
I'm going to try your idea.
2016-02-26 14:16 GMT+01:00 Robin East
<[email protected]<mailto:[email protected]>>:
Whilst I can think of other ways to do it I don’t think they would be
conceptually or syntactically any simpler. GraphX doesn’t have the concept of
built-in vertex properties which would make this simpler - a vertex in GraphX
is a Vertex ID (Long) and a bunch of custom attributes that you assign. This
means you have to find a way of ‘pushing’ the vertex degree into the graph so
you can do comparisons (cf a join in relational databases) or as you have done
create a list and filter against that (cf filtering against a sub-query in
relational database).
One thing I would point out is that you probably want to avoid
finalVerexes.collect() for a large-scale system - this will pull all the
vertices into the driver and then push them out to the executors again as part
of the filter operation. A better strategy for large graphs would be:
1. build a graph based on the existing graph where the vertex attribute is the
vertex degree - the GraphX documentation shows how to do this
2. filter this “degrees” graph to just give you 0 degree vertices
3 use graph.mask passing in the 0-degree graph to get the original graph with
just 0 degree vertices
Just one variation on several possibilities, the key point is that everything
is just a graph transformation until you call an action on the resulting graph
-------------------------------------------------------------------------------
Robin East
Spark GraphX in Action Michael Malak and Robin East
Manning Publications Co.
http://www.manning.com/books/spark-graphx-in-action
On 26 Feb 2016, at 11:59, Guillermo Ortiz
<[email protected]<mailto:[email protected]>> wrote:
I'm new with graphX. I need to get the vertex without out edges..
I guess that it's pretty easy but I did it pretty complicated.. and inefficienct
val vertices: RDD[(VertexId, (List[String], List[String]))] =
sc.parallelize(Array((1L, (List("a"), List[String]())),
(2L, (List("b"), List[String]())),
(3L, (List("c"), List[String]())),
(4L, (List("d"), List[String]())),
(5L, (List("e"), List[String]())),
(6L, (List("f"), List[String]()))))
// Create an RDD for edges
val relationships: RDD[Edge[Boolean]] =
sc.parallelize(Array(Edge(1L, 2L, true), Edge(2L, 3L, true), Edge(3L, 4L,
true), Edge(5L, 2L, true)))
val out = minGraph.outDegrees.map(vertex => vertex._1)
val finalVertexes = minGraph.vertices.keys.subtract(out)
//It must be something better than this way..
val nodes = finalVertexes.collect()
val result = minGraph.vertices.filter(v => nodes.contains(v._1))
What's the good way to do this operation? It seems that it should be pretty
easy.
