Is there an equivalent of the stack and unstack functions (for type dataset) that works for type double?

Hi Matlab experts,

I'm new to Matlab. I'm usually an R user, but I'm moving up to the big leagues in terms of data size, so here I am at the Matlab help forum. I have a giant sparse predictor matrix (200 million cells) that I am trying to convert to the proper format for regression. To perform any operations on this matrix in a reasonable amount of time it's necessary to exploit its sparsity by declaring it sparse with code like data=sparse(data). The functions 'stack' and 'unstack' in the statistics package do exactly the reformatting I need. But to use them, I need to convert my 'sparse matrix' into a 'dataset', which is no longer treated as sparse. So 'stack' and 'unstack' take way too long. Are there equivalent functions that I can feed a sparse matrix into as input? Or is there a way to get Matlab to treat a dataset as sparse?

Thanks a lot for any help,

Zach