Github user tillrohrmann commented on a diff in the pull request:
https://github.com/apache/flink/pull/1078#discussion_r39253000
--- Diff:
flink-staging/flink-ml/src/main/scala/org/apache/flink/ml/math/SparseVector.scala
---
@@ -85,6 +85,34 @@ case class SparseVector(
}
}
+ /** Returns the outer product (a.k.a. Kronecker product) of `this`
+ * with `other`. The result is given in
[[org.apache.flink.ml.math.SparseMatrix]]
+ * representation.
+ *
+ * @param other a Vector
+ * @return the [[org.apache.flink.ml.math.SparseMatrix]] which equals
the outer product of `this`
+ * with `other.`
+ */
+ override def outer(other: Vector): SparseMatrix = {
+ val numRows = size
+ val numCols = other.size
+
+ val otherIndices = other match {
+ case sv @ SparseVector(_, _, _) => sv.indices
+ case dv @ DenseVector(_) => (0 until dv.size).toArray
+ }
+
+ val entries = for {
+ i <- indices
+ j <- otherIndices
+ value = this(i) * other(j)
--- End diff --
It might make sense to directly operate on the `SparseVector's` data array
because every `apply` call entails a binary search and, thus, having a
complexity of `O(log n)`. The same holds true for the `other` vector if it is a
`SparseVector`.
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