Github user hhbyyh commented on a diff in the pull request:
https://github.com/apache/spark/pull/17940#discussion_r116139038
--- Diff: mllib/src/main/scala/org/apache/spark/mllib/linalg/Matrices.scala
---
@@ -992,7 +992,20 @@ object Matrices {
new DenseMatrix(dm.rows, dm.cols, dm.data, dm.isTranspose)
case sm: BSM[Double] =>
// There is no isTranspose flag for sparse matrices in Breeze
- new SparseMatrix(sm.rows, sm.cols, sm.colPtrs, sm.rowIndices,
sm.data)
+
+ // Some Breeze CSCMatrices may have extra trailing zeros in
+ // .rowIndices and .data, which are added after some matrix
+ // operations for efficiency.
+ //
+ // Therefore the last element of sm.colPtrs would no longer be
+ // coherent with the size of sm.rowIndices and sm.data
+ // despite sm being a valid CSCMatrix.
+ // We need to truncate both arrays (rowIndices, data)
+ // to the real size of the vector sm.activeSize to allow valid
conversion
+
--- End diff --
Maybe we can add some if else here, since slice will copy the array and
often that's not needed.
Please refer to
https://github.com/scalanlp/breeze/blob/master/math/src/main/scala/breeze/linalg/CSCMatrix.scala#L130
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