Github user tillrohrmann commented on a diff in the pull request:
https://github.com/apache/flink/pull/629#discussion_r29319548
--- Diff:
flink-staging/flink-ml/src/main/scala/org/apache/flink/ml/math/DenseVector.scala
---
@@ -80,6 +80,27 @@ case class DenseVector(val data: Array[Double]) extends
Vector with Serializable
data(index) = value
}
+ /** Returns the dot product of the recipient and the argument
+ *
+ * @param other a Vector
+ * @return a scalar double of dot product
+ */
+ override def dot(other: Vector): Double = {
+ require(size == other.size, "The size of vector must be equal.")
+
+ other match {
+ case SparseVector(_, otherIndices, otherData) =>
+ otherIndices.map(i => data(i) * otherData(i)).sum
--- End diff --
this won't work because the ```otherIndices``` array does not contain the
indices into the ```otherData``` array. ```otherData``` contains all non-zero
elements in a condensed manner. The original indices of the elements are then
contained in ```otherIndices```. So the non-zero elements (tuple of index and
value) are computed by ```0 to otherData.size map ( i => (otherIndices(i),
otherData(i))```.
To calculate the dot product with a ```DenseVector``` something like
```otherIndices.zipWithIndex.map((otherIndex, index) => data(otherIndex) *
otherData(i)).sum```
should work.
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