filling a matrix with Scala library breeze

Question

I'm new to Scala and I'm having a mental block on a seemingly easy problem. I'm using the Scala library breeze and need to take an array buffer (mutable) and put the results into a matrix. This... should be simple but? Scala is so insanely type casted breeze seems really picky about what data types it will take when making a DenseVector. This is just some prototype code, but can anyone help me come up with a solution? Right now I have something like...

//9 elements that need to go into a 3x3 matrix, 1-3 as top row, 4-6 as middle row, etc)
val numbersForMatrix: ArrayBuffer[Double] = (1, 2, 3, 4, 5, 6, 7, 8, 9) 
//the empty 3x3 matrix
var M: breeze.linalg.DenseMatrix[Double] = DenseMatrix.zeros(3,3)

In breeze you can do stuff like M(0,0) = 100 and set the first value to 100 this way, You can also do stuff like: M(0, 0 to 2) := DenseVector(1, 2, 3) which sets the first row to 1, 2, 3 But I cannot get it to do something like...

var dummyList: List[Double] = List(1, 2, 3) //this works
var dummyVec = DenseVector[Double](dummyList) //this works
M(0, 0 to 2) := dummyVec //this does not work

and successfully change the first row to the 1, 2,3. And that's with a List, not even an ArrayBuffer.

Am willing to change datatypes from ArrayBuffer but just not sure how to approach this at all... could try updating the matrix values one by one but that seems like it would be VERY hacky to code up(?).

Note: I'm a Python programmer who is used to using numpy and just giving it arrays. The breeze documentation doesn't provide enough examples with other datatypes for me to have been able to figure this out yet. Thanks!

Answer 1

Breeze is, in addition to pickiness over types, pretty picky about vector shape: DenseVectors are column vectors, but you are trying to assign to a subset of a row, which expects a transposed DenseVector:

M(0, 0 to 2) := dummyVec.t