bugfix

  }

  agg_X <- do.call(rbind, lapply(1:length(tmp), function(k){tmp[[k]][[3]]}))

  # experimental

  # cast to sparse matrix

  agg_X <- as(agg_X, 'sparseMatrix')

  # print(length(tmp))

  # print(dim(agg_X))

  # transpose expression matrix:

  print(class(agg_X))

  agg_X <- Matrix::t(agg_X)

  colnames(agg_X) <- bcs