[Tex/LaTex] Use a LaTeX expression in a knitr figure caption

knitr

I am writing an .Rnw document in RStudio. I would like to be able to use latex expressions in Figure captions created by knitr.

First a code chunk for the caption:

<<cap_4, echo=FALSE>>=
cap <- "My figure. 
Some \textit{italics}. 
A reference to another figure: \ref{fig:other-fig}.
"
@

Now the plot chunk:

<<my-plot, echo=FALSE, fig.cap=cap>>=
ggplot(aes(x = x, y = y), data = data)
@

This fails to correctly render the italics or reference in the figure caption. Instead I get only part of the text (minus the first letter of the expression), e.g. instead of

A reference to another figure: 1.

I get

A reference to another figure: ef{fig:other-fig}.

Is it possible to use latex expressions in a knitr caption?

Best Answer

You need to escape the slash, so that R doesn't treat the \r as a symbol to interpret:

\\ref{fig:other-fig}

Option 1: Using `knit_child()` with inline R code

Say your setup is like the following. In the same directory, you have:

`graph.R`

## ---- graph
library(ggplot2)
CarPlot <- ggplot() +
    stat_summary(data= mtcars,
                 aes(x = factor(gear),
                     y = mpg
                 ),
                 fun.y = "mean",
                 geom = "bar"
                 )
CarPlot

`chapter1.Rnw`

Hey, look, a graph (Figure~\ref{fig:graph})!

<<graph, echo=FALSE, message=FALSE, fig.lp='fig:', out.width='.5\\linewidth', fig.align='center', fig.cap="A graph", fig.pos='h!'>>=
@

`main.Rnw`

\documentclass{article}

\begin{document}

<<external-code, echo=FALSE, cache=FALSE>>=
read_chunk('./graph.R')
@

\Sexpr{knit_child('chapter1.Rnw')}

\end{document}

Then, you can knit the main.Rnw file and compile the resulting .tex file with either pdflatex or xelatex.

The output is:

enter image description here

Note that you can also read the external .R file from the child .Rnw file.

So, the following would have worked just as well.

`chapter1-mod.Rnw`

<<external-code, echo=FALSE, cache=FALSE>>=
read_chunk('./graph.R')
@

Hey, look, a graph (Figure~\ref{fig:graph})!

<<graph, echo=FALSE, message=FALSE, fig.lp='fig:', out.width='.5\\linewidth', fig.align='center', fig.cap="A graph", fig.pos='h!'>>=
@

`main-mod.Rnw`

\documentclass{article}

\begin{document}

\Sexpr{knit_child('chapter1-mod.Rnw')}

\end{document}

Option 2: Using chunk option `child`

Assuming you have graph.R and chapter1.Rnw from above in the same directory, then your main.Rnw should be:

\documentclass{article}

\begin{document}

<<external-code, echo=FALSE, cache=FALSE>>=
read_chunk('./graph.R')
@

<<child-demo, child='chapter1.Rnw'>>=
@

\end{document}

Note that you can also read the external .R file from within the child document in this case, too.

So, assuming you had graph.R and chapter1-mod.Rnw from above in the same directory, then your main-mod.Rnw file should be:

\documentclass{article}

\begin{document}

<<child-demo, child='chapter1-mod.Rnw'>>=
@

\end{document}

[Tex/LaTex] Special characters in knitr generated figure caption

The answer (I found) is pretty simple. knitr/R will pass to TeX special characters if correctly escaped (backslashed). It is also probably necessary to use double-quotes " " instead of single quotes ' '

\documentclass{article}
\usepackage{subfig}
\begin{document}

<<fig-sub, fig.cap="Three \\textit{plots}", fig.subcap=c("Erd\\H{o}s-R\\'enyi", "Barab\\'asi-Albert"), out.width='.30\\linewidth',dev='tikz',sanitize=TRUE>>=
library(ggplot2)

x<-1:10
y<-rnorm(10)

ggplot(data.frame(x,y), aes(x,y)) + geom_line()
ggplot(data.frame(y,x), aes(y,x)) + geom_line()
@

\end{document}

Best Answer

Related Solutions

[Tex/LaTex] Building TeX file from knitr Rnw as child of larger parent TeX file to use R objects and output

Option 1: Using knit_child() with inline R code

graph.R

chapter1.Rnw

main.Rnw

chapter1-mod.Rnw

main-mod.Rnw

Option 2: Using chunk option child