Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

mention options in importing vign #3578

merged 2 commits into from May 31, 2019
Changes from all commits
File filter

Filter by extension

Filter by extension

Failed to load comments.
Jump to
Jump to file
Failed to load files.
Diff view
Diff view
@@ -122,9 +122,15 @@ The case for `:=` is slightly different, because `:=` is interpreted as a functi

If you don't mind having `id` and `grp` registered as variables globally in your package namespace you can use `?globalVariables`. Be aware that these notes do not have any impact on the code or its functionality; if you are not going to publish your package, you may simply choose to ignore them.

## Care needed when providing and using options

Common practice by R packages is to provide customization options set by `options(name=val)` and fetched using `getOption("name", default)`. Function arguments often specify a call to `getOption()` so that the user knows (from `?fun` or `args(fun)`) the name of the option controlling the default for that parameter; e.g. `fun(..., verbose=getOption("datatable.verbose", FALSE))`. All `data.table` options start with `datatable.` so as to not conflict with options in other packages. A user simply calls `options(datatable.verbose=TRUE)` to turn on verbosity. This affects all calls to `fun()` other the ones which have been provided `verbose=` explicity; e.g. `fun(..., verbose=FALSE)`.

The option mechanism in R is _global_. Meaning that if a user sets a `data.table` option for their own use, that setting also affects code inside any package that is using `data.table` too. For an option like `datatable.verbose`, this is exactly the desired behavior since the desire is to trace and log all `data.table` operations from wherever they originate; turning on verbosity does not affect the results. Another unique-to-R and excellent-for-production option is R's `options(warn=2)` which turns all warnings into errors. Again, the desire is to affect any warning in any package so as to not missing any warnings in production. There are 6 `datatable.print.*` options and 3 optimization options which do not affect the result of operations, either. However, there is one `data.table` option that does and is now a concern: `datatable.nomatch`. This option changes the default join from outer to inner. [Aside, the default join is outer because outer is safer; it doesn't drop missing data silently.] Some users prefer inner join to be the default and we provided this option for them. However, a user setting this option can unintentionally change the behavior of joins inside packages that use `data.table`. Accordingly, in v1.12.4, we have started the process to deprecate the `datatable.nomatch` option. It is the only `data.table` option with this concern.

## Troubleshooting

If you face any problems in this process, before trying to ask questions or reporting issues, please confirm that the problem is reproducible in a clean R session using the R console: `R CMD check`.
If you face any problems in creating a package that uses data.table, please confirm that the problem is reproducible in a clean R session using the R console: `R CMD check`.

Some of the most common issues developers are facing are usually related to helper tools that are meant to automate some package development tasks, for example, using `roxygen` to generate your `NAMESPACE` file from metadata in the R code files. Others are related to helpers that build and check the package. Unfortunately, these helpers sometimes have unintended/hidden side effects which can obscure the source of your troubles. As such, be sure to double check using R console (run R on the command line) and ensure the import is defined in the `DESCRIPTION` and `NAMESPACE` files following the [instructions](#DESCRIPTION) [above](#NAMESPACE).