How can I center a Sweave verbatim chunk?

Question

I have a very simple sweave chunk with two lines, like this:

<<results=verbatim>>==
quantile(foo$bar)
@

How can I center this element? I've tried embracing the chunk with \begin{center} to no avail.

Answer 1

A verbatim environment by default has the width equal to the text width. Thus you cannot center it: the trailing whitespace is included in the line.

Fortunately, Sweave.sty uses fancyvrb package internally. Sweave defines three environments, for the input, output and code, using fancyvrb in the following way:

\DefineVerbatimEnvironment{Sinput}{Verbatim}{fontshape=sl}
\DefineVerbatimEnvironment{Soutput}{Verbatim}{}
\DefineVerbatimEnvironment{Scode}{Verbatim}{fontshape=sl}

Now fancyvrb has several environments. One which is helpful in your case is BVerbatim: the text is put into a box with the width by default equal to the width of the longest line of the text. The resulting box can be centered.

Thus the following works:

\documentclass{article}
\usepackage{Sweave}
\pagestyle{empty}
\DefineVerbatimEnvironment{Soutput}{BVerbatim}{}
\begin{document}
\noindent\rule{\textwidth}{.1pt} % To show centering
\begin{center}
<<>>==
2+3
@
\end{center}
\end{document}

We redefined Soutput as BVerbatim, and the output is now centered:

Note that only the output is centered in this example. To center input, redefine Sinput as well.