> Unless you have a data.frame that is all numeric, but in that case one should probably be using a matrix in the first place.

They still have their advantages with row/column labels, NaN handling etc. These are not operations I am speculating about by the way. I am most familiar with pandas and the dataframe there has transpose, dot product operations and almost all column operations have their correspondence in rows (i.e. you either sum(axis=0) or sum(axis=1)).