> str(t)
*** target data.frame ***
Target Name:  mtcars 
'data.frame':	6 obs. of  11 variables:
 $ mpg : num  21 21 22.8 21.4 18.7 18.1
 $ cyl : num  6 6 4 6 8 6
 $ disp: num  160 160 108 258 360 225
 $ hp  : num  110 110 93 110 175 105
 $ drat: num  3.9 3.9 3.85 3.08 3.15 2.76
 $ wt  : num  2.62 2.88 2.32 3.21 3.44 ...
 $ qsec: num  16.5 17 18.6 19.4 17 ...
 $ vs  : num  0 0 1 1 0 1
 $ am  : num  1 1 1 0 0 0
 $ gear: num  4 4 4 3 3 3
 $ carb: num  4 4 1 1 2 1
 - attr(*, "target_name")= symbol mtcars
*** treat_var***
gear
*** pop_data data.frame ***
'data.frame':	32 obs. of  11 variables:
 $ mpg : num  21 21 22.8 21.4 18.7 18.1 14.3 24.4 22.8 19.2 ...
 $ cyl : num  6 6 4 6 8 6 8 4 4 6 ...
 $ disp: num  160 160 108 258 360 ...
 $ hp  : num  110 110 93 110 175 105 245 62 95 123 ...
 $ drat: num  3.9 3.9 3.85 3.08 3.15 2.76 3.21 3.69 3.92 3.92 ...
 $ wt  : num  2.62 2.88 2.32 3.21 3.44 ...
 $ qsec: num  16.5 17 18.6 19.4 17 ...
 $ vs  : num  0 0 1 1 0 1 0 1 1 1 ...
 $ am  : num  1 1 1 0 0 0 0 0 0 0 ...
 $ gear: num  4 4 4 3 3 3 3 4 4 4 ...
 $ carb: num  4 4 1 1 2 1 4 2 2 4 ...
 - attr(*, "target_name")= symbol mtcars
 - attr(*, "pop_data_name")= symbol target
*** pop_treat_var ***
gear
*** treat_grps ***
 Total:
	 4 3 5