So, I really think this one is pretty cool. We spend much of our time in R making graphs with data, but what if you have a theory that you’d like to express graphically? Something like what I’ll call “economics-style” graphs, illustrating, for example, the Solow growth model, a production–possibility frontier, or an indifference curve?

Well, rest assured that R can produce those, too, and it’s made simple by the bezier() function from Hmisc (Hmisc does a lot of other interesting things, but this is what you got in today’s Advent CalendaR slot). Bézier curves are a workhorse of vector graphics, and if you’re not familiar with them, I encourage you to become so, with this beautiful interactive demo and with this more detailed interactive demo.

The Gist shows you how to use Bézier curves to replicate Wikipedia’s Supply-and-Demand graph, and is pretty heavily commented, but I’ll add a few notes:

- Generating a Bézier curve with pre-specified x and y vectors takes some trial-and-error. Fortunately, it is usually a fun puzzle and it’s very quick to test. Just think of each point as “pulling” the curve toward itself.
- The script defines a hacky little function called approxIntersection(), which is intended to let you input two (x, y) vectors and will output their approximate intersection. This probably doesn’t work well in a lot of cases, and I would be interested in hearing of anyone’s less hacky solutions.
- Earlier drafts of this code required a bit of ggplot2 theme-wrangling, but with the release of ggplot2 0.9.3, theme_classic now produces the exact look I was going for.

*Related*

To

**leave a comment** for the author, please follow the link and comment on their blog:

** is.R()**.

R-bloggers.com offers

**daily e-mail updates** about

R news and

tutorials on topics such as:

Data science,

Big Data, R jobs, visualization (

ggplot2,

Boxplots,

maps,

animation), programming (

RStudio,

Sweave,

LaTeX,

SQL,

Eclipse,

git,

hadoop,

Web Scraping) statistics (

regression,

PCA,

time series,

trading) and more...

If you got this far, why not

__subscribe for updates__ from the site? Choose your flavor:

e-mail,

twitter,

RSS, or

facebook...