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From danielblazevski <...@git.apache.org>
Subject [GitHub] flink pull request: [FLINK-3996] Add addition, subtraction and multiply by s...
Date Tue, 31 May 2016 12:16:26 GMT
Github user danielblazevski commented on a diff in the pull request:

    https://github.com/apache/flink/pull/2052#discussion_r65170092
  
    --- Diff: flink-libraries/flink-ml/src/main/scala/org/apache/flink/ml/math/SparseVector.scala
---
    @@ -175,10 +176,21 @@ case class SparseVector(
     
         java.util.Arrays.binarySearch(indices, 0, indices.length, index)
       }
    +
    +  def + (other: Vector): Vector = (this.asBreeze + other.asBreeze).fromBreeze
    +
    +  def - (other: Vector): Vector = (this.asBreeze - other.asBreeze).fromBreeze
    +
    +  def * (scalar: Double): Vector = (scalar * this.asBreeze).fromBreeze
    +
    --- End diff --
    
    Remark:  when I put `+` and `-` in the `Vector` Trait to avoid duplication of code, it
works fine, but not when I add the `*` method to the `Vector` Trait.  I get errors even when
using `+` when I add the `*` method in `Vector`, namely:
    
    ```
    Error:(86, 68) could not find implicit value for evidence parameter of type org.apache.flink.ml.math.BreezeVectorConverter[T]
      def + (other: Vector): Vector = (this.asBreeze + other.asBreeze).fromBreeze
                                                   ^
    ```
    
    This error does not appear if I have `+` and `-` in Vector.scala and keep `*` duplicated
in both DenseVector.scala and SparseVector.scala.  Found it weird then to have `+` and `-`
in Vector.scala and `*` separate.  This is why I decided to duplicate the code in DenseVector
and SparseVector.  Happy to hear if anyone knows of a way to avoid this.


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