Sorting a DenseMatrix object

[davide...@googlemail.com]

Hi there,
I am using Breeze library for a machine learning project.
I have the need to sort a DenseMatrix based on the content of the first column.
Is there a class/function which would allow me to do that?

Many thanks,
Davide

[David Hall]

I don't think there's anything built in to help you with that. I have aspirations of something like dm(*, ::).sortBy(r => r(0)), but that doesn't exist just yet.

For now, probably (0 until dm.rows).map(dm(_, ::)).sortBy(r => r(0))

-- David

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[davide...@googlemail.com]

Hi David,
thanks for prompt reply and sorry for my late reply :).

I think I sorted it out creating a function which converts the DenseMatrix to a List of DenseVector, sorts the DenseVectors and then it re-converts the List of DenseVectors back to a DenseMatrix.
The code snippet is below, i still need to test it properly though (just run a quick test as of today).

I am new with scala, so I am not sure if this is the best way.

object sortDenseMatrix {

  def apply(inputMatrix: DenseMatrix[Double], colIndex: Int): DenseMatrix[Double] = {

    val sortingList: List[DenseVector[Double]] = (0 until inputMatrix.rows).map(i => inputMatrix(i,::).t).toList.sortBy {x => x(0)}
    val outputMatrix = DenseMatrix(sortingList.map(_.toArray):_*)                                                            
   
    return outputMatrix
 
  }
}

Davide

[David Hall]

looks great. the .toList is probably unnecessary, though.

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[davide...@googlemail.com]

Thanks for the advice David :)