tab_r.ltx

\captionsetup[table]{labelformat=empty,skip=1pt}
\begin{longtable}{lrlclllr}
\toprule
 & num & char & fctr & date & time & datetime & currency \\ 
\midrule
\multicolumn{1}{l}{grp\_a} \\ 
\midrule
row\_1 & 1.111e-01 & apricot & one & 2015-01-15 & 13:35 & 2018-01-01 02:22 & 49.950 \\ 
row\_2 & 2.222e+00 & banana & two & 2015-02-15 & 14:40 & 2018-02-02 14:33 & 17.950 \\ 
row\_3 & 3.333e+01 & coconut & three & 2015-03-15 & 15:45 & 2018-03-03 03:44 & 1.390 \\ 
row\_4 & 4.444e+02 & durian & four & 2015-04-15 & 16:50 & 2018-04-04 15:55 & 65100.000 \\ 
\midrule
\multicolumn{1}{l}{grp\_b} \\ 
\midrule
row\_5 & 5.550e+03 & NA & five & 2015-05-15 & 17:55 & 2018-05-05 04:00 & 1325.810 \\ 
row\_6 & NA & fig & six & 2015-06-15 & NA & 2018-06-06 16:11 & 13.255 \\ 
row\_7 & 7.770e+05 & grapefruit & seven & NA & 19:10 & 2018-07-07 05:22 & NA \\ 
row\_8 & 8.880e+06 & honeydew & eight & 2015-08-15 & 20:20 & NA & 0.440 \\ 
 \bottomrule
\end{longtable}