[R] for loop over dataframe without indices

[Gabor Grothendieck]

One can perform a for loop without indices over the columns
of a dataframe like this:

   for( v in df ) ... some statements involving v ...

Is there some way to do this for rows other than using indices:

   for( i in 1:nrow(df) ) ... some statements involving df[i,] ...

If the dataframe had only numeric entries I could transpose it
and then do it over columns but what about the general case?