Author: Achim Zeileis

# CRAN Task Views Documentation

#### Achim Zeileis

## Overview

For more details on how to use task views and how to contribute to them, see the repository of the CRAN Task Views Initiative.

## Format

The file format for CRAN task views leverages the R/Markdown format (see Xie, Allaire, Grolemund 2019) so that standard Markdown can be used for formatting and structuring the text and a handful of special R functions are provided to link to CRAN packages, other task views, GitHub projects, etc.

> In `ctv` versions prior to 0.9-0 (released in December 2021), task views used an XML-based format (introduced in Zeileis 2005, R News, 5(1), 39-40 [PDF]). See below for converting task views from the old XML-based format to the new R/Markdown format.

The format is mostly self-explanatory and is illustrated below using an excerpt from the `Econometrics` task view which is hosted on CRAN at https://CRAN.R-project.org/view=Econometrics and maintained on GitHub at https://github.com/cran-task-views/Econometrics/.

    ---
    name: Econometrics
    topic: Econometrics
    maintainer: Achim Zeileis, Grant McDermott, Kevin Tappe
    email: Achim.Zeileis@R-project.org
    version: 2022-09-13
    source: https://github.com/cran-task-views/Econometrics/
    ---

    Base R ships with a lot of functionality useful for (computational) econometrics,
    in particular in the stats package. This functionality is complemented by many
    packages on CRAN, a brief overview is given below. There is also a certain
    overlap between the tools for econometrics in this view and those in the task
    views on `r view("Finance")`, `r view("TimeSeries")`, and
    `r view("CausalInference")`.

    Further information can be formatted with standard Markdown syntax, e.g., for
    _emphasizing text_ or showing something really important in **bold face**.
    R/Markdown syntax with special functions can be used to link to a standard
    package like `r pkg("mlogit")` or an important "core" package like
    `r pkg("AER", priority = "core")`.

    ### Links
    - Articles: [Special Volume on "Econometrics in R" in JSS (2008)](https://www.jstatsoft.org/v27/)
    - [The Title of a Relevant Homepage](https://path/to/homepage/)

The document structure consists of three main blocks: (1) Some metainformation is given in the YAML header at the beginning (separated by lines with `---`), followed by (2) the information in the main text, and (3) a concluding special section called `### Links`.

## Details

### Metainformation

The metainformation needs to provide the following elements:

- `name` gives the name of the task view in CamelCase. This is used as the identifier for installing the view and as the name for the Markdown file, e.g., `Econometrics.md`, and the auto-generated HTML file, e.g., `Econometrics.html`. Hence, it should be not too long (typically 1-3 words) and contain no special characters like spaces, hyphens, etc.

- `topic` is a plain text specification of the topic of the task view. In the example above it is identical to the `name` but is often a somewhat longer and more detailed title (in title case).

- `maintainer` gives the name(s) of the maintainer(s) in a comma-separated list. The principal contact should be listed first, followed by a couple of further co-maintainers that help keeping the task view up to date.

- `email` is the e-mail address of the principal contact or possibly a dedicated mailing list shared by the co-maintainers.

- `version` is specified by a date in ISO 8601 format (yyyy-mm-dd).

- Additionally, there may be optional elements: `source` can be used to link to the source repository (typically on GitHub) and `url` for the URL of the published task view, respectively. The latter is inserted automatically for the official task views on CRAN.

### Main text

The information in the main text should be a short description of the packages, explaining which packages are useful for which tasks. Standard Markdown format can be used to structure the document with sections, itemized and enumerated lists, bold face, italics, etc.

Additionally, short R code chunks with special functions are used for linking to resources in the same repository: `pkg()` for regular packages, `pkg(..., priority = "core")` for important “core” packages, and `view()` for related task views. A convenience function `doi()` creates links for DOIs (digital object identifiers).

- The distinction between “regular” and “core” packages is only important for the installation of CRAN task views because the user can specify whether all packages (default) or only the most important core packages should be installed (with all their dependencies).

- If a core package is mentioned several times in the document, it is sufficient to indicate `priority = "core"` for one of the occurrences.

- Rather than linking to another task view as a whole, e.g., `view("Econometrics")`, it is also possible to link to specific sections of that view, e.g., `view("Econometrics", "Instrumental variables")`.

Moreover, code projects in other repositories can be linked by using the functions:

- `bioc()` for Bioconductor packages at https://www.Bioconductor.org/.
- `github()` for GitHub projects at https://github.com/.
- `rforge()` for R-Forge projects at https://R-Forge.R-project.org/.
- `gcode()` for projects in the Google Code archive at https://Code.Google.com/archive/.
- `ohat()` for Omegahat packages at https://www.Omegahat.net/.

Note however that CRAN task views are intended mainly for packages on CRAN (as the name conveys). Thus, links to other repositories should be used for important packages/projects but not list all potentially relevant repositories. Also, it is not necessary to list the GitHub projects for all listed CRAN packages as these are typically provided on the package’s CRAN web page.

### Links

All CRAN packages included with the `pkg()` function will be listed in a dedicated list below the information text when rendering the HTML version of the task view. Also, the task views as well as packages/projects in other repositories will be included automatically in the list of links at the end of the HTML version.

Finally, additional links - e.g., to books, papers, blogs, interest groups, mailing lists, etc. - can be included in the `### Links` section at the end of the file in a standard itemized list. As explained above this list of links will be complemented automatically with links generated from the functions `view()`, `bioc()`, `github()`, etc.

## Working with task view files in R

To check whether a task view file has been formatted properly it can be read into R and printed. This should display the metainformation and the list of packages. Subsequently, it can be rendered to an HTML page and displayed in a browser for checking whether the information text is processed correctly. Finally, the function `check_ctv_packages()` can be used to check whether some of the listed packages are actually not available on CRAN or not currently maintained (archived).

For illustration, the code below employs the `Econometrics.md` file shipped within the `ctv` package. Instead a local `MyTopic.md` with resulting `MyTopic.html` could be used as well.

    library("ctv")
    file.copy(system.file("ctv", "Econometrics.md", package = "ctv"), "Econometrics.md")
    ctv2html("Econometrics.md", cran = TRUE)
    browseURL("Econometrics.html")
    check_ctv_packages("Econometrics.md")

Note that the code above is intended for authors of CRAN task views. For end-users the functions `ctv()`, `available.views()`, `install.views()`, and `update.views()` are relevant. See https://github.com/cran-task-views/ctv/ for more details.

## Dealing with archived packages

The CRAN packages listed in task views should ideally be maintained actively, so that improved versions are released by the corresponding maintainers in case the daily CRAN checks discover any issues.

However, it is not straightforward to test for active maintenance fully automatically and even actively maintained packages may be temporarily archived on CRAN. Hence, the following strategy is adopted:

- When a CRAN package from a task view is archived, it is still listed in the task view like before. It is only flagged as archived in the text and not installed automatically anymore by `install.views()` and `update.views()`.

- If the package is still archived after (more than) 60 days, CRAN creates an issue in the GitHub repository of the task view (as in this example).

- At this point the task view maintainers can decide to

  - exclude the package from the task view immediately, e.g., if they feel it had not been that relevant and/or not been updated in a very long time;
  - reach out to the package maintainer to help with releasing an improved version; or
  - wait some more for an improved version, e.g., when they see that the package maintainers already started addressing the problem.

- If the package is still archived after (more than) 100 days, CRAN follows up on the issue and requests removal of the package from the task view. (For sufficiently relevant packages it may be sensible to replace the `pkg()` link by a `github()` link in the task view.)

## Converting the legacy XML format to R/Markdown

The `ctv` package provides an (unexported) R function to facilitate the transition from the legacy XML format for the task view files to the new R/Markdown format described above. Simply using

    ctv:::ctv_xml_to_rmd("MyTopic.ctv")

will create a `MyTopic.md` file from the `.ctv` file. This should do most necessary transformations automatically. However, it is recommended to thoroughly check the resulting file and improve it as appropriate. To check the resulting HTML output use

    ctv2html("MyTopic.md")
    browseURL("MyTopic.html")

Note that one important difference between the XML and R/Markdown format is that the “package list” does not need to be listed separately anymore, it is auto-generated from the “info” text. Similarly, the “links” just need to provide those links that are not auto-generated from the “info” text.