Function str_data_frame 

pub(crate) fn str_data_frame(val: &RValue) -> Option<String>

Format str() output for a data.frame using tabled for alignment.

Produces output like R’s str():

'data.frame':  N obs. of  M variables:
 $ col1: int  1 2 3 ...
 $ col2: chr  "a" "b" "c" ...