The Rnw document that confused several people in R-help.

test.Rnw

\documentclass{article}
\begin{document}

<<setup, include=FALSE, cache=FALSE>>=
library(knitr)
library(ggplot2)
@

\title{Knitr and ggplot2}
\author{Daniel Haugstvedt}

\maketitle

There are four plots in this article. Figure \ref{fig:plot-figHeight} uses
the argument fig.height=2.5 while Figures \ref{fig:plot-figWidth}
used both fig.height=2.5 and fig.width=3. The later option makes the font
too big.

An alternative approach is used in Figures  \ref{fig:plot-figOutWidthBig}
and
 \ref{fig:plot-figOutWidthSmall}. There the argument out.width is set to
 12 and 8 cm respectively. This stops the problem of excessively large fonts
 for figures with smaller width, but there is still no consistency
 across plots in terms of font size.

<<plot-figHeight, fig.height=2.5, fig.cap="Density plot with no fig.width argument", fig.pos='ht'>>=
df = data.frame(x = rnorm(100), y = 1:100)
ggplot(df, aes(x = x)) +
  geom_histogram(aes(y = ..density..),
                 binwidth = 1, colour = "black", fill = "white") +
  xlab("Improvement, %") +
  ylab("Density") +
  theme_classic()
@

<<plot-figWidth, echo=FALSE, fig.height=2.5, fig.width = 3, fig.cap="Density plot with fig.width=3", fig.pos='ht'>>=
ggplot(df, aes(x = x)) +
  geom_histogram(aes(y = ..density..),
                 binwidth = 1, colour = "black", fill = "white") +
  xlab("Improvement, %") +
  ylab("Density") +
  theme_classic()
@

<<plot-figOutWidthBig, echo=FALSE, fig.height=2.5, out.width = "12cm", fig.cap="Density plot with out.width=12cm", fig.pos='ht'>>=
ggplot(df, aes(x = x)) +
  geom_histogram(aes(y = ..density..),
                 binwidth = 1, colour = "black", fill = "white") +
  xlab("Improvement, %") +
  ylab("Density") +
  theme_classic()
@

<<plot-figOutWidthSmall, echo=FALSE, fig.height=2.5, out.width = "8cm", fig.cap="Density plot with out.width=8cm", fig.pos='ht'>>=
ggplot(df, aes(x = x)) +
  geom_histogram(aes(y = ..density..),
                 binwidth = 1, colour = "black", fill = "white") +
  xlab("Improvement, %") +
  ylab("Density") +
  theme_classic()
@

\end{document}