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title: "Exporting tidying methods from a package"
author: "Alex Hayes"
date: "`r Sys.Date()`"
output: rmarkdown::html_vignette
vignette: >
%\VignetteIndexEntry{Exporting tidying methods from a package}
```{r setup, include = FALSE}
collapse = TRUE,
eval = FALSE,
comment = "#>"
NOTE: This vignette describes how extend the broom generics in an external package. To *use* the broom generics in an external you can `Import` broom as you would normally.
This guide describes how to extend the `tidy()`, `glance()` and `augment()` generics. broom recently started re-exporting these generics from the `modelgenerics` package. `modelgenerics` is not yet on CRAN, nor is the version of broom that uses `modelgenerics`. You'll need to wait for these CRAN releases (timeline TBD at the moment) before release your package to CRAN if you extend broom in the manner described here.
If you are a package developer, the best place to include `tidy()`, `glance()` or `augment()` methods is in your own package. To do this, you'll need to:
1. Re-export the `tidy()`, `glance()` and `augment()` generics from the `modelgenerics` package.
2. Implement appropriate tidying methods.
3. Test the tidying methods
You can re-export generics from broom itself, but `modelgenerics` is a much lighter dependency.
The [dustpan]( package demonstrates use of `modelgenerics` and `modeltests`, and you may find it helpful to browse.
## Re-exporting `tidy()`, `glance()` and `augment()` generics
First you'll need to add the [modelgenerics]( package to `Imports`. We recommend using the [usethis]( package for this:
usethis::use_package("modelgenerics", "Imports")
Next you'll need to re-export the appropriate tidying methods. If you plan to implement a `glance()` method, for example, you can re-export the glance generic by adding the following somewhere in your package
#' @importFrom modelgenerics glance
#' @export
Run `devtools::document()` for these changes to take effect.
Note: please do not define `tidy()`, `glance()` or `augment()` generics in your package. This will result in namespace conflicts whenever your package is used along other packages that also export tidying methods.
## Implement appropriate tidying methods
This part is mostly up to you, although there's lots of advice in `vignette("adding-tidiers")`.
## Testing
Now that you have a tidying method, you'll want to test it. In addition to testing the specific functionality of your tidying methods, you should also pass the standardized tests exported from [modeltests](
To import these tests you'll need to add `modeltests` to `Suggests`, which you can accomplish with:
# once modeltests makes its way onto CRAN:
# usethis::use_package("modeltests", "Suggests")
# until then:
You can then write tests for your tidiers following the advice in `vignette("adding-tidiers")`.
If you're run `devtools::test()` and `devtools::check()` and didn't fail any tests or set off R CMD Check ERRORS, WARNINGS or NOTES, you're done!
## F.A.Q.
### Should I `Import` or `Suggest` `broom` or `broom.mixed`?
If you are using tidiers from broom, such as `tidy.lm()`, then you will need to depend on `broom`, probably via `Imports`:
use_package("broom", "Imports")
Similarly, if you are using tidiers from `broom.mixed`, you'll need to `Import` `broom.mixed`.
You can import `broom.mixed` separately from `broom`, or you can mix and match them however you want.
### I don't want to depend on `modelgenerics`. Can I re-export `tidy()`, `glance()` and `augment()` from `broom`?
Yes, this is fine.
### What do I do if my tidiers don't pass the tests?
If you are introducing new arguments or column names in output, you'll need to make a pull request to `modeltests` to add the new argument/column names to the glossary of allowed names.
If you'd like to change the test specifications, or if you find a bug in the tests, open an issue in `modeltests`.
As a last resort, you can set `strict = FALSE` to run only a bare minimum of tests. This is not recommended.
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