file16eb1613831f.R

library(dplyr)

mtcars %>%
  group_by(cyl) %>%
  summarize(mean(disp))

# # A tibble: 3 × 2
# cyl `mean(disp)`
# <dbl>        <dbl>
#   1     4     105.1364
#   2     6     183.3143
#   3     8     353.1000