Filling a THnD or THnSparse using `Draw` or `RDataFrame`

I am having a look to the documentation of classes THnD and THnSparse. I see in the documentation that this objects are filled as a traditional TH1D histogram, using Fill. So I could just iterate and fill. But there is a more straight forward way to do this?

I see for example inside RDataFrame there is a method .HistoND that I imagine it returns a THnD.

However, how could I initialise a THnSparse object that seems to be more suited for data with many zeros?

If I try:

auto hN = dataFrame.HistoND( ... );

It works, but how do I cast the auto to the object I want?

Ok, (edit) I found that I could create a THnd:

root [17] THnD *hNd = new THnD(*dd)
(THnD *) 0x5556cbb7e770
root [18] hNd->GetEntries()
(double) 10000.000

But not a THnSparse with the same technique:

root [19] THnSparse *hSparse = new THnSparse(*dd)
ROOT_prompt_19:1:26: error: allocating an object of abstract class type 'THnSparse'
THnSparse *hSparse = new THnSparse(*dd)
/programas/root/6.26.06/include/THnSparse.h:61:20: note: unimplemented pure virtual method 'GenerateArray' in 'THnSparse'
   virtual TArray* GenerateArray() const = 0;
root [20] 
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