How to replace elements of a breeze matrix in Scala based on some condition?

Question

I am working with 2 dimensional Breeze matrices in Scala. At some point I have to do element-wise division of two matrices. Some elements in the denominator matrix can be zero, resulting into NaNs in the result.

I can loop through the matrix dimensions and replace the 0.0s with something >0.

But is there a simpler or Scala idiomatic solution for this?

Answer 1

Step-by-step:

• With example matrix:

  val dm = DenseMatrix((1.0, 0.0, 3.0), (0.0, 5.0, 6.0))
  

• Find out which elements are equal to 0.0:

  dm :== 0.0
  

  breeze.linalg.DenseMatrix[Boolean] =
  false  true   false
  true   false  false
  

• Slice the matrix:

  dm(dm :== 0.0)
  

  breeze.linalg.SliceVector[(Int, Int),Double] = breeze.linalg.SliceVector@2b
  

• Use sliced matrix for replacement:

  dm(dm :== 0.0) := 42.0
  

  breeze.linalg.Vector[Double] = breeze.linalg.SliceVector@2b
  

• Check the matrix:

  dm
  

  breeze.linalg.DenseMatrix[Double] =
  1.0   42.0  3.0
  42.0  5.0   6.0