A.count B.reduceByKeyAndWidow C.countByValue D.reduceByKey
A.RowMatrix B.IndexedRowMatrix C.Matrix D.CoordinateMatrix
A.val dm:Matrix=Matrices.dense(3,2,Array(0.0,3.0,0.0,2.0,0.0,6.0)) B.val dm:Matrix=Matrices.sparse(3,2,Array(0.0,2.0,3.0,0.0,0.0,6.0)) C.val sm:Matrix=Matrices.sparse(3,2,Array(0,1,2),Array(1,0,1),Array(2,3,6)) D.val sm:Matrix=Matrices.dense(3,2,Array(0,1,2),Array(1,0,1),Array(2,3,6))