# [R] Sweave: looping over mixed R/LaTeX code

Dieter Menne dieter.menne at menne-biomed.de
Sat Jun 14 09:30:04 CEST 2008

Stephan Kolassa <Stephan.Kolassa <at> gmx.de> writes:

>
> I would like to loop over a medium amount of Sweave code, including both R
and LaTeX chunks. Is there any way to

Stephan noted that \newcommand was not expanded, so after re-reading I
realized that my comment was a bit short. After all, when I had encountered
the problem the first time, I remember some headaches when thinking about
the hen and the egg.

Below is a full example. The trick is to generate the newcommand and
parameter with R. This method is especially helpful when you have a dozen or
so of laboratory parameter that all have to be plotted, tabled, tested
between groups, and summarized. I write the chapter only once, when I works
I wrap everything with a newcommand. Default Sweave figure creation is
not possible, but doing it explicitely with a pdf/dev.off is not much
more complicated.

Dieter

% ----------------------------------
\documentclass{article} %

\usepackage{Sweave}
\SweaveOpts{echo=FALSE}

\newcommand\bloodp[3]{
\subsection{Patient #1}
For patient #1, the mean value of systolic pressure was #2~mmHg,
the diastolic pressure was #3~mmHg.
\begin{figure}[!htb]%
\begin{center}%
\includegraphics{histo#1}%
\caption{Histogram of systolic blood pressure for patient #1.}%
\label{fig:histo#1}%
\end{center}%
\end{figure}%
\clearpage % Better use FloatBarrier here
}

\begin{document}
\section{Blood Pressure}

<<results=tex>>=
n=100
dt = data.frame(subj=sample(1:3,n,TRUE),
syst=round(rnorm(n,120,10)),dia=round(rnorm(n,80,10)))

# could also use tapply here
for (i in 1:3) {
dt1 = dt[dt$subj==i,] cat("\\bloodp{",i,"}{", round(mean(dt1$syst)),"}{",
round(mean(dt1$dia)),"}\n",sep="") pdf(paste("histo",i,".pdf",sep="")) hist(dt1$syst,main="",xlab="Blood pressure")
dev.off()
}
@

\end{document}