Referring to other figures from within a chunk

Question

Inside the plot generated in a chunk in a knitr/LaTeX document I want to position a text string with a reference to a particular figure elsehwere in the document, something like "See Fig. 10", based on the label of a that particular figure, lets say "fig:sim1". So I wrote the following R function which reads the .aux file of the LaTeX-document I'm writing and extracts the counter of the figure matching a specific label

ref <- function(label) {
  lines <- scan("mismatch-final.aux","character",sep="\n")
  line <- grep(paste("\\{",label,"\\}",sep=""),lines,value=TRUE)
  strsplit(strsplit(line,"\\{\\{")[[1]][2],"\\}\\{")[[1]][1]
}

I can then generate the desired text string from within the chunk and place it inside the plot with something like

text(5,10,paste("See Fig.~",ref("fig:sim1")))

This should work but perhaps there is a cleaner way of doing this? Also, is there a way to get at the .aux filename from within the chunk such that the ref function above would be made more general?

Yihui Xie Yihui Xie · Accepted Answer · 2014-05-28T02:21:04

Another way to do that is to use the tikzDevice package and TikZ plots, so you can write raw LaTeX expressions in your plot, e.g

\begin{figure}
....
\caption{Simulation of something. \label{fig:sim1}}
\end{figure}

<<test, dev='tikz', external=FALSE>>=
plot(rnorm(10), rnorm(10))
text(0, 0, 'See Fig \\ref{fig:sim1}')
@

Depending on the complexity of your plot, this chunk may take a few seconds to compile each time. The plot is saved as a LaTeX file, and any LaTeX commands will work in it.

Referring to other figures from within a chunk

1 Answers