I am trying to implement a subclass of tbl to tweak the way how my data is printed. The code is part of a package.
I have read the documentation and used these lines:
as_data_test <- function(...) {
tibble::new_tibble(..., class = "data_test")
}
tbl_format_header.data_test <- function(x, setup, ...) {
cli::style_italic("A Data Test = ", setup$tbl_sum)
}
Then I use devtools::load_all(".") to load the package. But when I try to print my data_test object, it does not use the custom tbl_format_header function:
devtools::load_all(".")
# i Loading datatesteR
as_data_test(mtcars)
# # A tibble: 32 x 11
# mpg cyl disp hp drat wt qsec vs am gear carb
# <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl>
# 1 21 6 160 110 3.9 2.62 16.5 0 1 4 4
# 2 21 6 160 110 3.9 2.88 17.0 0 1 4 4
# 3 22.8 4 108 93 3.85 2.32 18.6 1 1 4 1
# 4 21.4 6 258 110 3.08 3.22 19.4 1 0 3 1
# 5 18.7 8 360 175 3.15 3.44 17.0 0 0 3 2
# 6 18.1 6 225 105 2.76 3.46 20.2 1 0 3 1
# 7 14.3 8 360 245 3.21 3.57 15.8 0 0 3 4
# 8 24.4 4 147. 62 3.69 3.19 20 1 0 4 2
# 9 22.8 4 141. 95 3.92 3.15 22.9 1 0 4 2
# 10 19.2 6 168. 123 3.92 3.44 18.3 1 0 4 4
# # i 22 more rows
# # i Use `print(n = ...)` to see more rows
As you can see only the default header is printed. Placing a browser call in tbl_format_header.data_test confirms that my method is never dispatched. If I put the same code directly into an R console, everything works like a charm.
How would I get the custom printing in my devtools workflow?
First, more generally, if you want to implement a method for an S3 generic, you need to export it. If you are using roxygen2, you can add #' @export above your method for class tbl_sum. When you run devtools::document(), this will add the following to your NAMESPACE file:
S3method(tbl_format_header,data_test)
Second (to the contrary of the aforementioned), this will not work for tbl_sum as it does not exist in the namespace of your package. In this case, you can use roxygen2's @exportS3Method:
#' @exportS3Method pillar::tbl_format_header
tbl_format_header.data_test <- function(x, setup, ...) {
cli::style_italic("A Data Test = ", setup$tbl_sum)
}
This will modify your NAMESPACE to:
S3method(pillar::tbl_format_header,data_test)
Source: R packages, chapter 11.9