Machine Learning with Spark - Second Edition

Types of matrices

In Scala, we will use the Breeze library to represent a matrix. A matrix can be represented as a dense or a CSC matrix.

• Dense matrix: A dense matrix is created with a constructor method call. Its elements can be accessed and updated. It is a column major, and can be transposed to convert to row major.

        val a = DenseMatrix((1,2),(3,4))           println("a : n" + a)          val m = DenseMatrix.zeros[Int](5,5)         The columns of a matrix can be accessed as Dense Vectors, and            the rows as  Dense Matrices.           println( "m.rows :" + m.rows + " m.cols : "  + m.cols)           m(::,1)          println("m : n" + m) 

• Transposing a matrix: Transposing a matrix means swapping its rows and columns. The transpose of a P × Q matrix, written MT, is a Q × P matrix such that ...