# Math Expressions with Facets in ggplot2

In this post I show how we can use math expressions to label the panels in facets to produce the following plot:

The updated version of ggplot2 V 2.0 has improved the way we can label panels in facet plots with the use of a generic labeller function. The latex2exp package has made it much easier to write expressions in `R`

.

You will need to load the following packages for the code below to work:

I have posted some sample data in a GitHub Gist which you can import into your `R`

session using the `source_gist`

function from the devtools package:

Then we create a labelling function which takes as input a string and prepends to it. Note that `latex2exp::TeX`

is the workhorse function that parses syntax so that `R`

understands it. Otherwise it becomes very messy to try and write more complex math expressions in `R`

.

The code to produce the plot above is given by:

Note that we need to provide the `default = label_parsed`

argument to the `facet_wrap`

function so that it interprets the result from the `appender`

function as math expressions.