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From: danielblazevski <git@git.apache.org>
To: issues@flink.incubator.apache.org
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Subject: [GitHub] flink pull request: [FLINK-3996] Add addition, subtraction and multiply by s...
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Message-Id: <20160531121627.19E5BDFB74@git1-us-west.apache.org>
Date: Tue, 31 May 2016 12:16:26 +0000 (UTC)
archived-at: Tue, 31 May 2016 12:16:30 -0000

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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