[Rcpp-devel] Additional constructors for DataFrame

[Davor Cubranic]

Although DataFrame is a subclass of List, it's missing a few handy 
constructors that List (i.e., Vector) have, such as "(const int& size)" 
to pre-allocate the space for it.

Yes, I can always create a List first and convert it to a DataFrame 
afterwards, but this actually doesn't copy some attributes from the 
original List. (I noticed it for "row.names", but there may be others.)

I'd be happy to submit a small patch, but wanted to check here first if 
I'm missing any potential problems around these constructors and that's 
the reason why they are not available for DataFrames.

Thanks,

Davor