dplyr group by intervals of 3

d %>% mutate( ints = cut(v1 ,breaks = 11)) %>% 
   group_by(ints) %>% 
   summarise( mean.v2 = mean(v2) , mean.v3 = mean(v3) )

library(lubridate)
x <- ymd_hms("2009-08-03 12:25:59.23")
floor_date(x, unit = "3minutes")