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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.spark.graphx.lib
import scala.reflect.ClassTag
import org.apache.spark.graphx._
/** Connected components algorithm. */
object ConnectedComponents {
/**
* Compute the connected component membership of each vertex and return a graph with the vertex
* value containing the lowest vertex id in the connected component containing that vertex.
*
* @tparam VD the vertex attribute type (discarded in the computation)
* @tparam ED the edge attribute type (preserved in the computation)
*
* @param graph the graph for which to compute the connected components
*
* @return a graph with vertex attributes containing the smallest vertex in each
* connected component
*/
def run[VD: ClassTag, ED: ClassTag](graph: Graph[VD, ED]): Graph[VertexId, ED] = {
val ccGraph = graph.mapVertices { case (vid, _) => vid }
def sendMessage(edge: EdgeTriplet[VertexId, ED]): Iterator[(VertexId, VertexId)] = {
if (edge.srcAttr < edge.dstAttr) {
Iterator((edge.dstId, edge.srcAttr))
} else if (edge.srcAttr > edge.dstAttr) {
Iterator((edge.srcId, edge.dstAttr))
} else {
Iterator.empty
}
}
val initialMessage = Long.MaxValue
val pregelGraph = Pregel(ccGraph, initialMessage, activeDirection = EdgeDirection.Either)(
vprog = (id, attr, msg) => math.min(attr, msg),
sendMsg = sendMessage,
mergeMsg = (a, b) => math.min(a, b))
ccGraph.unpersist()
pregelGraph
} // end of connectedComponents
}
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