[GitHub] [spark] zhengruifeng commented on issue #26982: [SPARK-30329][ML] add iterator/foreach methods for Vectors

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zhengruifeng commented on issue #26982: [SPARK-30329][ML] add iterator/foreach methods for Vectors
URL: https://github.com/apache/spark/pull/26982#issuecomment-568413966
 
 
   Performace test for `SparseVector.iterator`:
   ```scala
   import org.apache.spark.ml.linalg._
   import scala.util.Random
   
   val rand = new Random(123)
   
   val size = 100000000
   val nnz = 1000000
   
   val indices = Array.fill(nnz * 2)(rand.nextInt(size).abs).distinct.take(nnz).sorted
   val values = Array.fill(nnz)(rand.nextDouble)
   
   val sv = Vectors.sparse(size, indices, values)
   
   
   scala> val start = System.currentTimeMillis; Seq.range(0, 10).foreach{_ => Iterator.range(0, size).map{sv.apply}.sum }; val end = System.currentTimeMillis; end - start
   start: Long = 1577092459234
   end: Long = 1577092537941
   res5: Long = 78707
   
   scala> val start = System.currentTimeMillis; Seq.range(0, 10).foreach{_ => sv.iterator.map(_._2).sum }; val end = System.currentTimeMillis; end - start
   start: Long = 1577092546174
   end: Long = 1577092579521
   res6: Long = 33347
   ```
   
   In this case, impl based on internal cursors are about 2.4X faster than directly using `apply` method.

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