---
title: "Manipulating Citations with cffr"
description: Learn how to modify `cff` objects.
toc: true
bibliography: REFERENCES.bib
link-citations: true
vignette: >
  %\VignetteIndexEntry{Manipulating Citations with cffr}
  %\VignetteEngine{quarto::html}
  %\VignetteEncoding{UTF-8}
knitr:
  opts_chunk:
    collapse: true
    comment: "#>"
    warning: false
    message: true
---

```{r}
#| include: false
library(cffr)
```

**cffr** is a tool whose target audience are **R** package developers. The main
goal of **cffr** is to create a `CITATION.cff` file using the metadata
information of the following files:

-   Your `DESCRIPTION` file.
-   If available, the citation information located in `inst/CITATION`.

## What is a `CITATION.cff` file?

[Citation File Format (CFF)](https://citation-file-format.github.io/)
[@druskat_citation_2021] (v1.2.0) are plain text files with human- and
machine-readable citation information for software (and data sets). Code
developers can include them in their repositories to let others know how to
correctly cite their software.

This format is gaining popularity within the software citation ecosystem.
Recently,
[GitHub](https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/about-citation-files),
[Zenodo](https://citation-file-format.github.io/#/supported-by-zenodo-) and
[Zotero](https://citation-file-format.github.io/#/supported-by-zotero-) have
fully supported this citation format [@druskat_stephan_making_2021].

GitHub support is of special interest:

<figure>

![](tweet-1.png){.quarto-figure .quarto-figure-center fig-align="center"
width="400"}

```{=html}
<figcaption class="blockquote-footer">Nat Friedman (@natfriedman) July 27, 2021</figcaption>
</figure>
```

See [Customize your repository/About CITATION
files](https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/about-citation-files)
for more information.

## Creating a `CITATION.cff` file for my R package

Creating a `CITATION.cff` file with **cffr** is straightforward. You simply need
to run `cff_write()`:

```{r}
#| label: setup
#| eval: false
library(cffr)

cff_write()

# You are done!
```

Under the hood, `cff_write()` performs the following tasks:

-   It extracts the metadata using `cff_create()`.
-   Optionally modifies it with `cff_modify()`.
-   Writes a `CITATION.cff` file.
-   Validates the result using `cff_validate()`.

Congratulations! Now you have a full `CITATION.cff` file for your **R** package.

## Modifying your `CITATION.cff` file

You can easily customize the `cff` object (a custom class of **cffr**) using the
coercion system provided in the package, as well as the `keys` argument.

We create a `cff` object using `cff()` (for example purposes only) and then add
or modify its contents.

### Adding new fields

```{r}
#| label: newfields
newobject <- cff()

newobject
```

The valid keys of the [Citation File Format schema version
1.2.0](https://github.com/citation-file-format/citation-file-format/blob/main/schema-guide.md)
can be displayed with `cff_schema_keys()`:

```{r}
#| label: validkeys
cff_schema_keys()
```

In this case, we add `url`, `version`, and `repository`. We also overwrite the
`title` key. We add these arguments to `cff_modify()`:

```{r}
#| label: modify
modobject <- cff_modify(
  newobject,
  url = "https://ropensci.org/",
  version = "0.0.1",
  repository = "https://github.com/ropensci/cffr",
  # If the field is already present, it would be overridden
  title = "Modifying a 'cff' object"
)

modobject

# Validate against the schema

cff_validate(modobject)
```

### Persons and references

**cffr** provides two functions that convert `person` and `bibentry` objects
(see `?person` and `?bibentry`) according to the [Citation File Format
schema](https://github.com/citation-file-format/citation-file-format/blob/main/schema-guide.md).

Following the previous example, we first add a new author. To do that, we need
to extract the current author of the package and append the coerced person:

```{r}
#| label: includeauthor
# Valid person keys

cff_schema_definitions_person()

# Create the person

chiquito <- person(
  "Gregorio",
  "Sánchez Fernández",
  email = "fake@email2.com",
  comment = c(
    alias = "Chiquito de la Calzada",
    city = "Malaga",
    country = "ES",
    ORCID = "0000-0000-0000-0001"
  )
)

chiquito

# To cff
chiquito_cff <- as_cff_person(chiquito)
chiquito_cff

# Append to previous authors

newauthors <- c(modobject$authors, chiquito_cff)
newauthors

newauthorobject <- cff_modify(modobject, authors = newauthors)

newauthorobject

cff_validate(newauthorobject)
```

Now, we may want to add `references` to our data. On the following example, we
would add two references, one created with `bibentry()` and another with
`citation()`:

```{r}
#| label: parsingcits
# Valid reference keys

cff_schema_definitions_refs()

# Auto coercion from another R package
base_r <- citation("base")

bib <- bibentry(
  "Book",
  title = "This is a book",
  author = "Lisa Lee",
  year = 1980,
  publisher = "McGraw Hill",
  volume = 2
)

refs <- c(base_r, bib)

refs

# Now to cff

refs_cff <- as_cff(refs)

refs_cff
```

Now the process is similar to the example with `person`: we just modify our
`cff` object:

```{r}
#| label: references
finalobject <- cff_modify(newauthorobject, references = refs_cff)

finalobject

cff_validate(finalobject)
```

### Create your modified `CITATION.cff` file

The results can be written with `cff_write()`:

```{r}
#| label: write
# For example
tmp <- tempfile(fileext = ".cff")

see_res <- cff_write(finalobject, outfile = tmp)

cat(readLines(tmp), sep = "\n")
```

And finally we can read our created `CITATION.cff` file using `cff_read()`:

```{r}
#| label: read
reading <- cff_read(tmp)

reading
```

Note that `cff_write()` also has the `keys` param, so the workflow can be
simplified as:

```{r}
allkeys <- list(
  "url" = "https://ropensci.org/",
  "version" = "0.0.1",
  "repository" = "https://github.com/ropensci/cffr",
  # If the field is already present, it would be overridden
  title = "Modifying a 'cff' object",
  authors = newauthors,
  references = refs_cff
)

tmp2 <- tempfile(fileext = ".cff")

res <- cff_write(cff(), outfile = tmp2, keys = allkeys)

res
```

```{r}
#| include: false
# Clean temps
unlink(tmp)
unlink(tmp2)
```

## References
