Matrix Transpose on RowMatrix in Spark

Question

Suppose I have a RowMatrix.

1. How can I transpose it. The API documentation does not seem to have a transpose method.
2. The Matrix has the transpose() me

Answer 1

You can use BlockMatrix, which can be created from an IndexedRowMatrix:

BlockMatrix matA = (new IndexedRowMatrix(...).toBlockMatrix().cache();
matA.validate();

BlockMatrix matB = matA.transpose();

Then, can be easily put back as IndexedRowMatrix. This is described in the spark documentation.