Github user SereneAnt commented on a diff in the pull request:
https://github.com/apache/spark/pull/18693#discussion_r128635631
--- Diff: graphx/src/main/scala/org/apache/spark/graphx/lib/PageRank.scala
---
@@ -199,10 +199,10 @@ object PageRank extends Logging {
require(sources.max <= Int.MaxValue.toLong,
s"This implementation currently only works for source vertex ids at
most ${Int.MaxValue}")
val zero = Vectors.sparse(sources.size, List()).asBreeze
- val sourcesInitMap = sources.zipWithIndex.map { case (vid, i) =>
+ val sourcesInitMap: Map[VertexId, BV[Double]] =
sources.zipWithIndex.map { case (vid, i) =>
val v = Vectors.sparse(sources.size, Array(i), Array(1.0)).asBreeze
(vid, v)
- }.toMap
+ }(collection.breakOut)
--- End diff --
The principles are the same,
`sources.zipWithIndex.map {...}' allocates a collection of tuples, `.toMap`
then uterates and converts them into the map (hehe).
breakOut is the implementation of CanBuildFrom, the implicit parameter
passed to `Traversable.map` method. Once used, it allows populating newborn map
directly, without intermediate collection of tuples.
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