CODEWITHSUNDEEP
scalascala-breeze
SnarkShark
SnarkShark

Reputation: 380

Updating scala breeze matrix for point with x,y coordinates (NOT length of rows and cols)

I'm new to Scala (Python background) and trying to implement a Quadtree for my sparse data and attempting to use Breeze to do so (although if you have a better suggestion, I'm totally open to it).

My problem is this: I need to know how to update a matrix at (x,y) without recursing through simply i <- 0 until matrix.rows because I don't have the values for all the rows and columns, I only have specific xs and ys. If this is unclear here's what I mean: In the breeze documentation, you normally see something like this

val r = new scala.util.Random(100)
    for(i <-0 until Matrix.rows)
        for(j <- 0 until Matrix.cols)
            Matrix(i,j) = r.nextInt
    return Matrix

This is fine and dandy if I had a value for EVERY value in the matrix, but I don't. Instead what I'm working with is something like this.

val points: Array[Double] = Array(3.0, 5.0, 8.0)
val xs: Array[Double] = Array(2.0, 5.0, 6.0)
val ys: Array[Double] = Array(3.0, 4.0, 6.0)

where I want matrix(2,3) = 3.0

Where I know that my matrix should be a 6x6 matrix DenseMatrix[Double](6,6).

Assuming that I begin with a matrix of zeros (DenseMatrix.zeros(6,6)) how can I insert my points using my xs and ys rather than .rows and .cols?

I have tried this: (where emptym is a 6x6 matrix of zeros)

val matrix = for {
     | x <- xs
     | y <- ys
     | p <- points
     | } yield (emptym(x.toInt,y.toInt) = p)

which gives me all kinds of errors :/

I was thinking maybe I could do this with some kind of map function, because I want to return a val for this but I'm new enough to scala that I cant quite figure out how to do this.

Please help me figure this out. Thanks! :)

Edit -- Ideally, I'm hoping for a more FP solution that doesn't have to loop through the matrix and update it. I'd like to create a new matrix. I'm thinking something like this, but can't get it to work:

val newMatrix = oldMatrix.map(xs, ys, points => oldMatirx(x,y) = point)

Upvotes: 0

Views: 575

Answers (1)

akuiper
akuiper

Reputation: 215067

You can use the update method, where you can pass the row number, col number and the value to update a cell in the matrix:

val mat = DenseMatrix.zeros[Double](6,6)
for (i <- 0 until xs.length) {
  mat.update(xs(i).toInt - 1, ys(i).toInt - 1, points(i))
}

Print the matrix out:

for (i <- 0 until mat.rows){
  for(j <- 0 until mat.cols) {
    print(mat(i, j) + " ")
  }
  println()
}

0.0 0.0 0.0 0.0 0.0 0.0 
0.0 0.0 3.0 0.0 0.0 0.0 
0.0 0.0 0.0 0.0 0.0 0.0 
0.0 0.0 0.0 0.0 0.0 0.0 
0.0 0.0 0.0 5.0 0.0 0.0 
0.0 0.0 0.0 0.0 0.0 8.0

Upvotes: 1

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