code: private static DMatrix csr(Frame f, int[] chunksIds, Vec.Reader[] vecs, Vec.Reader w, Vec.Reader respReader, // for setupLocal
                                 int nRows, DataInfo di, float[] resp, float[] weights)
          throws XGBoostError {
          return csr(null, -1, -1, f, chunksIds, vecs, w, respReader, nRows, di, resp, weights);
      }
docs: **************************************************************************************************************
  ********************************** DMatrix creation for sparse (CSR) matrices *********************************
  **************************************************************************************************************