r - How do I access all the elements of a data.frame using group_by (dplyr)? -

suppose have data.frame 'df':

 speed dist lan       4    2 "bra"       4   10 "bra"       7    4 "bra"       7   22 "col"       8   16 "col"       9   10 "col"      10   18 "fin"              ... 

i want realize operations on speed , dist groupin_by lan, example, try print values. how do that?

i've tried manner cannot achieve success:

df %>%   group_by(lan) %>%   (function(.) {       print(.$speed)       print(.$dist)   }) 

you should use do @r2evans suggested in comments above. better return original data.frame, can continue work it. in case instance might want calculate mean speed , mean dist after:

df %>%   group_by(lan) %>%   do({     cat("lan = ", .$lan[1], "\n")     print(.$speed)     print(.$dist)     .   }) %>%    summarise(mean(speed), mean(dist)) 

and can show output, here's example mtcars.

mtcars %>%    group_by(cyl) %>%    do({cat("cyl = ", .$cyl[1], "\n")       print(.$mpg)        print(.$wt)        .}) %>%    summarise(mean(mpg), mean(wt)) ## cyl =  4  ##  [1] 22.8 24.4 22.8 32.4 30.4 33.9 21.5 27.3 26.0 30.4 21.4 ##  [1] 2.320 3.190 3.150 2.200 1.615 1.835 2.465 1.935 2.140 1.513 2.780 ## cyl =  6  ## [1] 21.0 21.0 21.4 18.1 19.2 17.8 19.7 ## [1] 2.620 2.875 3.215 3.460 3.440 3.440 2.770 ## cyl =  8  ##  [1] 18.7 14.3 16.4 17.3 15.2 10.4 10.4 14.7 15.5 15.2 13.3 19.2 15.8  15.0 ##  [1] 3.440 3.570 4.070 3.730 3.780 5.250 5.424 5.345 3.520 3.435 3.840 3.845 3.170 3.570 ## source: local data frame [3 x 3] ##  ##   cyl mean(mpg) mean(wt) ## 1   4  26.66364 2.285727 ## 2   6  19.74286 3.117143 ## 3   8  15.10000 3.999214