In this post I show how we can use `$\LaTeX$`

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 `$\LaTeX$`

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:

```
data <- devtools::source_gist(id = "ed3caf50247cae8e3e1c", filename = "facet_data.R")$value
```

Then we create a labelling function which takes as input a string and prepends `$\log(\lambda_{\gamma})$`

to it. Note that `latex2exp::TeX`

is the workhorse function that parses `$\LaTeX$`

syntax so that `R`

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

.

```
appender <- function(string)
TeX(paste("$\\log(\\lambda_{\\gamma}) = $", string))
```

The code to produce the plot above is given by:

```
ggplot(data, aes(log(lambda.beta), ymin = lower, ymax = upper)) +
geom_errorbar(color = "grey") +
geom_point(aes(x = log(lambda.beta), y = mse),
colour = "red") +
theme_bw() +
facet_wrap(~lg, scales = "fixed",
labeller = as_labeller(appender,
default = label_parsed)) +
theme(strip.background = element_blank(),
strip.text.x = element_text(size = 14)) +
xlab(TeX("$\\log(\\lambda_{\\beta})$"))
```

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.