Big things come in small packages

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# Big things come in small packages
## Tips and tricks for your own R package
### Cosima Meyer
### 2021-11-13

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## Some words about me

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<img src="img/book.png" width=90 height=70>
<br><br><br>

<img src="img/lamp.png" width=90 height=90>
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.right-column[
**PhD** from the University of Mannheim, now working as a data scientist

<br><br><br>
**Co-founder** and **co-editor** of the data science blog [**Methods Bites**](https://www.mzes.uni-mannheim.de/socialsciencedatalab/)

<br><br><br><br><br>
**Maintainer** and **author** of the CRAN package [**overviewR**](https://cosimameyer.github.io/overviewR/)
]

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# Writing packages is like putting your function in a box
<br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br>

---
# What you need

--
One **function** (or some more)

```r
make_sum <- function(a, b) {
  c <- a + b
  return(c)
}
```

and the **following packages**:

```r
library(roxygen2) # In-Line Documentation for R 
library(devtools) # Tools to Make Developing R Packages Easier
library(testthat) # Unit Testing for R
library(usethis)  # Automate Package and Project Setup
```

---
# Set up your package with RStudio

`File` > `New Project...` > `New Directory` > `R Package`

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.center[![Popup window that shows up when opening a new package development process in RStudio](img/setup.png)]
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# Typical package structure

.center[![Setupt of a package structure showing the RStudio interface](img/setup2.png)]

`R/your_function.R` `\(\rightarrow\)` Where your functions live

`DESCRIPTION` `\(\rightarrow\)` Essential information on your package

`tests/` `\(\rightarrow\)` Where your tests live

`dev/` `\(\rightarrow\)` Development environment

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<span style="font-size:3em">**How it works in practice** </span>
<br><br><br>
<span style="font-size:3em">💻</span>

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# Important things

1) Write **unit tests**

```r
library(testthat)

# Test for outcome
expect_equal(make_sum(2, 3), 5)

expect_length(make_sum(2, 3), 1)

# Test for type
expect_type(make_sum(2, 3), "double")
```

[`{xpectr}`](https://github.com/LudvigOlsen/xpectr) helps you generate automatized unit tests

`\(\rightarrow\)` `devtools::test()` to run tests

2) Check **your package**

[`{devtools}`](https://devtools.r-lib.org) `\(\rightarrow\)` check whether it works on different operating systems

[`{goodpractice}`](http://mangothecat.github.io/goodpractice/)

`{inteRgrate}`

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# Important things

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<span style="font-size:1.5em">🥳</span> The steps on the last slide and much more is all in this [**checklist**](https://www.mzes.uni-mannheim.de/socialsciencedatalab/article/r-package/#section5)  
]
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.center[![Checklist for package submission](img/checklist.png)]
]

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# Debugging

Two important commands:

```r
browser()
```

--
Can be placed anywhere in your function and will stop the run of your function

--
<br><br><br>

```r
debug(FUNCTIONNAME)
```

--
Goes step-by-step through your function and allows you to inspect the output at each step

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<br><br><br>
# More resources

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*Writing a package*

- [How to write your own R package and publish it on CRAN (Cosima Meyer and Dennis Hammerschmidt)](https://www.mzes.uni-mannheim.de/socialsciencedatalab/article/r-package/)
- [R Packages (Hadley Wickham)](http://r-pkgs.had.co.nz/)
- [How to develop good R packages (for open science) (Maëlle Salmon)](https://masalmon.eu/2017/12/11/goodrpackages/)
- [devtools Cheat Sheet](https://rawgit.com/rstudio/cheatsheets/master/package-development.pdf)
- [Writing an R package from scratch (Hilary Parker)](https://hilaryparker.com/2014/04/29/writing-an-r-package-from-scratch/)
- [Your first R package in 1 hour (Shannon Pileggi)](https://www.pipinghotdata.com/talks/2020-10-25-your-first-r-package-in-1-hour/)
- [R package primer (Karl Broman)](https://kbroman.org/pkg_primer/)
]]
  
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*Other helpful things*

- [Checklist for R Package (Re-)Submissions on CRAN (Saskia Otto)](https://www.marinedatascience.co/blog/2020/01/09/checklist-for-r-package-re-submissions-on-cran/)
- [Continuous integration with GitHub Actions (Dean Attali )](https://deanattali.com/blog/migrating-travis-to-github/)
]]

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