I am trying to implement a subclass of a tibble which comes with a custom printing method. I figured that dplyr::group_by silently drops my custom class with the effect that my S3 printing methods are not dispatching anymore.
As I assume that this behaviour is a feature and not a bug, I was wondering what the canonical way of dealing with this should be? Overloading dplyr::group_by? Or am I overlooking something very fundamental here?
My expectation would be that the grouped my_tbl also displays my custom header:
library(tibble)
## Define a custom subclass of tbl
my_tbl <- function(x) {
new_tibble(x, class = "my_tbl")
}
## Define an own tbl_sum function
tbl_sum.my_tbl <- function(x) {
c("My Fancy Header" = "Whooaaaa!")
}
## Header is printed as it should
(mt <- my_tbl(mtcars %>% dplyr::slice(1L)))
# # My Fancy Header: Whooaaaa!
# mpg cyl disp hp drat wt qsec vs am gear carb
# <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl>
# 1 21 6 160 110 3.9 2.62 16.5 0 1 4 4
## However, not when we add a grouping structure
mt %>% dplyr::group_by(am)
# # A tibble: 1 × 11
# # Groups: am [1]
# mpg cyl disp hp drat wt qsec vs am gear carb
# <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl>
# 1 21 6 160 110 3.9 2.62 16.5 0 1 4 4
## Reason: group_by silently drops my custom class
class(mt) ##...vs...
# [1] "my_tbl" "tbl_df" "tbl" "data.frame"
class(mt %>% dplyr::group_by(am))
# [1] "grouped_df" "tbl_df" "tbl" "data.frame"
You'll need to implement a group_by() method for your class. From the dplyr extension vignette:
Note that group_by() and ungroup() don't use any of these generics and you'll need to provide methods for them directly, or rely on .by for per-operation grouping.