grouply.R

grouply <- function(f, ...) {
  groups <- lazyeval::lazy_dots(...)
  
  function(tbl, ...) {
    dplyr::group_by_(tbl, .dots = groups) %>%
      f(...) %>%
      dplyr::ungroup()
  }
}

mtcars %>% grouply(mutate, cyl, am)(n = n())