How to include ggplot graphics within Sweave

sweave_ggplot.Rnw

% compile with
%   R CMD Sweave sweave_ggplot.Rnw
%   pdflatex sweave_ggplot.tex
\documentclass[t,ucs,12pt,xcolor=dvipsnames]{beamer}
\usepackage{fancyvrb}

\title{A sample Sweave demo}
\author{Author name}
\date{}

% customize color code chunk (Scode = inline)
\definecolor{Sinput}{rgb}{0.75,0.19,0.19}
\definecolor{Soutput}{rgb}{0,0,0}
\definecolor{Scode}{rgb}{0.75,0.19,0.19}


\begin{document}
% default size for the sweaved graphics
\setkeys{Gin}{width=0.6\textwidth}
% default font size and color for R code
\DefineVerbatimEnvironment{Sinput}{Verbatim}
{formatcom = {\color{Sinput}},fontsize=\scriptsize}
\DefineVerbatimEnvironment{Soutput}{Verbatim}
{formatcom = {\color{Soutput}},fontsize=\footnotesize}
\DefineVerbatimEnvironment{Scode}{Verbatim}
{formatcom = {\color{Scode}},fontsize=\small}

\frame{\titlepage}

<<echo=false>>=
set.seed(101)
library(ggplot2)
library(ellipse)
@

\begin{frame}[fragile]
<<>>=
n <- 1000
x <- rnorm(n, mean=2)
y <- 1.5 + 0.4*x + rnorm(n)
df <- data.frame(x=x, y=y)

# take a bootstrap sample
df <- df[sample(nrow(df), nrow(df), rep=TRUE),]

xc <- with(df, xyTable(x, y))
df2 <- cbind.data.frame(x=xc$x, y=xc$y, n=xc$number)
df.ell <- as.data.frame(with(df, ellipse(cor(x, y), 
                                         scale=c(sd(x),sd(y)), 
                                         centre=c(mean(x),mean(y)))))
p1 <- ggplot(data=df2, aes(x=x, y=y)) + 
  geom_point(aes(size=n), alpha=.6) + 
  stat_smooth(data=df, method="loess", se=FALSE, color="green") + 
  stat_smooth(data=df, method="lm") +
  geom_path(data=df.ell, colour="green", size=1.2)
@
\end{frame}

\begin{frame}
  \begin{figure}
    \centering
<<fig=true,echo=false>>=
print(p1)
@
    \caption{Here goes the caption.}
    \label{fig:p1}
  \end{figure}
\end{frame}

\end{document}