knitr-manual.lyx

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knitr
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\begin_body

\begin_layout Standard
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status open

\begin_layout Plain Layout

<<setup, include=FALSE, cache=FALSE>>=
\end_layout

\begin_layout Plain Layout

## this is equivalent to 
\backslash
SweaveOpts{}
\end_layout

\begin_layout Plain Layout

opts_chunk$set(fig.path='figure/manual-', cache.path='cache/manual-', fig.align='ce
nter', fig.show='hold', par=TRUE)
\end_layout

\begin_layout Plain Layout

## I use = but I can replace it with <-; set code/output width to be 68
\end_layout

\begin_layout Plain Layout

options(replace.assign=TRUE, width=68)
\end_layout

\begin_layout Plain Layout

## tune details of base graphics (http://yihui.name/knitr/hooks)
\end_layout

\begin_layout Plain Layout

knit_hooks$set(par=function(before, options, envir){
\end_layout

\begin_layout Plain Layout

if (before && options$fig.show!='none') par(mar=c(4,4,.1,.1),cex.lab=.95,cex.axis=.9,mg
p=c(2,.7,0),tcl=-.3)
\end_layout

\begin_layout Plain Layout

})
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@
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\end_layout

\begin_layout Title
knitr: A General-Purpose Tool for Dynamic Report Generation in R
\end_layout

\begin_layout Author
Yihui Xie
\end_layout

\begin_layout Standard
The original paradigm of literate programming was brought forward mainly
 for software development, or specifically, to mix source code (for computer)
 and documentation (for human) together.
 Early systems include 
\begin_inset CommandInset href
LatexCommand href
name "WEB"
target "http://www.literateprogramming.com/web.pdf"

\end_inset

 and 
\begin_inset CommandInset href
LatexCommand href
name "Noweb"
target "http://www.cs.tufts.edu/~nr/noweb/"

\end_inset

; Sweave 
\begin_inset CommandInset citation
LatexCommand citep
key "leisch2002"

\end_inset

 was derived from the latter, but it is less focused on documenting software,
 instead it is mainly used for reproducible data analysis and generating
 statistical reports.
 The 
\series bold
knitr
\series default
 package 
\begin_inset CommandInset citation
LatexCommand citep
key "R-knitr"

\end_inset

 is following the steps of Sweave.
 For this manual, I assume readers have some background knowledge of Sweave
 to understand the technical details; for a reference of available options,
 hooks and demos, see the package homepage 
\begin_inset Flex URL
status collapsed

\begin_layout Plain Layout

http://yihui.name/knitr/
\end_layout

\end_inset

.
\end_layout

\begin_layout Section
Hello World
\end_layout

\begin_layout Standard
A natural question is why to reinvent the wheel.
 The short answer is that extending Sweave by hacking 
\family sans
SweaveDrivers.R
\family default
 in the 
\series bold
utils
\series default
 package is a difficult job to me.
 Many features in 
\series bold
knitr
\series default
 come naturally as users would have expected.
 Figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:cars-demo"

\end_inset

 is a simple demo of some features of 
\series bold
knitr
\series default
.
\end_layout

\begin_layout Standard
\begin_inset Float figure
wide false
sideways false
status open

\begin_layout Plain Layout
\begin_inset ERT
status open

\begin_layout Plain Layout

<<cars-demo,dev='tikz',fig.width=4,fig.height=2.8,out.width='.45
\backslash

\backslash
textwidth',message=FALSE,cache=TRUE>>=
\end_layout

\begin_layout Plain Layout

fit=lm(dist~speed,data=cars) # linear regression
\end_layout

\begin_layout Plain Layout

par(mar=c(4, 4, 1, .1), mgp=c(2,1,0))
\end_layout

\begin_layout Plain Layout

with(cars,plot(speed,dist,panel.last=abline(fit)))
\end_layout

\begin_layout Plain Layout

text(10,100,'$Y = 
\backslash

\backslash
beta_0 + 
\backslash

\backslash
beta_1x + 
\backslash

\backslash
epsilon$')
\end_layout

\begin_layout Plain Layout

library(ggplot2)
\end_layout

\begin_layout Plain Layout

qplot(speed, dist, data=cars)+geom_smooth()
\end_layout

\begin_layout Plain Layout

@
\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
\begin_inset CommandInset label
LatexCommand label
name "fig:cars-demo"

\end_inset

A simple demo of possible output in 
\series bold
knitr
\series default
: (1) multiple plots per chunk; (2) no need to 
\emph on
print()
\emph default
 objects in 
\series bold
ggplot2
\series default
; (3) device size is 
\begin_inset Formula $4\times2.8$
\end_inset

 (inches) but output size is adjusted to 
\family typewriter
.45
\backslash
textwidth
\family default
 in chunk options; (4) base graphics and 
\series bold
ggplot2
\series default
 can sit side by side; (5) use the 
\emph on
tikz()
\emph default
 device in 
\series bold
tikzDevice
\series default
 by setting chunk option 
\family typewriter
dev='tikz'
\family default
 (hence can write native LaTeX expressions in R plots); (6) code highlighting.
\end_layout

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Standard
I would have chosen to hide the R code if this were a real report, but here
 I show the code just for the sake of demonstration.
 If we type 
\emph on
qplot()
\emph default
 in R, we get a plot, and the same thing happens in 
\series bold
knitr
\series default
.
 If we draw two plots in the code, 
\series bold
knitr
\series default
 will show two plots and we do not need to tell it how many plots are there
 in the code in advance.
 If we set 
\family typewriter
out.width='.49
\backslash

\backslash
textwidth'
\family default
 in chunk options, we get it in the final output document.
 If we say 
\family typewriter
fig.align='center'
\family default
, the plots are centered.
 That's it.
 Many enhancements and new features will be introduced later.
 If you come from the Sweave land, you can take a look at the page of transition
 first: 
\begin_inset Flex URL
status collapsed

\begin_layout Plain Layout

http://yihui.name/knitr/demo/sweave/
\end_layout

\end_inset

.
\end_layout

\begin_layout Section
Design
\end_layout

\begin_layout Standard
The flow of processing an input file is similar to Sweave, and two major
 differences are that 
\series bold
knitr
\series default
 provides more flexibility to the users to customize the processing, and
 has many built-in options such as the support to a wide range of graphics
 devices and cache.
 Below is a brief description of the process:
\end_layout

\begin_layout Enumerate

\series bold
knitr
\series default
 takes an input file and automatically determines an appropriate set of
 
\begin_inset CommandInset href
LatexCommand href
name "patterns"
target "http://yihui.name/knitr/patterns"

\end_inset

 to use if they are not provided in advance (e.g.
 
\family sans
file.Rnw
\family default
 will use 
\family typewriter
knit_patterns$get('rnw')
\family default
);
\end_layout

\begin_layout Enumerate
a set of output 
\begin_inset CommandInset href
LatexCommand href
name "hooks"
target "http://yihui.name/knitr/hooks"

\end_inset

 will also be set up automatically according to the filename extension (e.g.
 use LaTeX environments or HTML elements to wrap up R results);
\end_layout

\begin_layout Enumerate
the input file is read in and split into pieces consisting of R code chunks
 and normal texts; the former will be executed one after the other, and
 the latter may contain global chunk options or inline R code;
\end_layout

\begin_layout Enumerate
for each chunk, the code is evaluated using the 
\series bold
evaluate
\series default
 package 
\begin_inset CommandInset citation
LatexCommand citep
key "R-evaluate"

\end_inset

, and the results may be filtered according to chunk options (e.g.
 
\family typewriter
echo=FALSE
\family default
 will remove the R source code)
\end_layout

\begin_deeper
\begin_layout Enumerate
if 
\family typewriter
cache=TRUE
\family default
 for this chunk, 
\series bold
knitr
\series default
 will first check if there are previously cached results under the cache
 directory before really evaluating the chunk; if cached results exist and
 this code chunk has not been changed since last run (use MD5 sum to verify),
 the cached results will be (lazy-) loaded, otherwise new cache will be
 built; if a cached chunk depends on other chunks (see the 
\family typewriter
dependson
\family default
 
\begin_inset CommandInset href
LatexCommand href
name "option"
target "http://yihui.name/knitr/options"

\end_inset

) and any one of these chunks has changed, this chunk must be forcibly updated
 (old cache will be purged)
\end_layout

\begin_layout Enumerate
there are six types of possible output from 
\series bold
evaluate
\series default
, and their classes are 
\family typewriter
character
\family default
 (normal text output), 
\family typewriter
source
\family default
 (source code), 
\family typewriter
warning
\family default
, 
\family typewriter
message
\family default
, 
\family typewriter
error
\family default
 and 
\family typewriter
recordedplot
\family default
; an internal S3 generic function 
\emph on
wrap()
\emph default
 is used to deal with different types of output, using output hooks defined
 in the object 
\family typewriter
knit_hooks
\end_layout

\begin_layout Enumerate
note plots are recorded as R objects before they are really saved to files,
 so graphics devices will not be opened unless plots have really been produced
 in a chunk
\end_layout

\begin_layout Enumerate
a code chunk is evaluated in a separate empty environment with the global
 environment as its parent, and all the objects in this environment after
 the evaluation will be saved if 
\family typewriter
cache=TRUE
\end_layout

\begin_layout Enumerate
chunk hooks can be run before and/or after a chunk
\end_layout

\end_deeper
\begin_layout Enumerate
for normal texts, 
\series bold
knitr
\series default
 will find out if there are chunk options set among them (e.g.
 
\family typewriter

\backslash
SweaveOpts{}
\family default
), and evaluate inline R code (e.g.
 
\family typewriter

\backslash
Sexpr{}
\family default
); the latter is involved with the 
\family typewriter
inline
\family default
 hook;
\end_layout

\begin_layout Standard
The hooks play important roles in 
\series bold
knitr
\series default
: this package makes almost everything accessible to the users.
 Consider the following extremely simple example which may demonstrate this
 freedom:
\end_layout

\begin_layout Standard
\begin_inset ERT
status open

\begin_layout Plain Layout

<<simple-example>>=
\end_layout

\begin_layout Plain Layout

1+1
\end_layout

\begin_layout Plain Layout

@
\end_layout

\end_inset


\end_layout

\begin_layout Standard
There are two parts in the final output: the source code 
\family typewriter
1 + 1
\family default
 and the output 
\family typewriter
[1] 2
\family default
; the comment characters 
\family typewriter
##
\family default
 are from the default chunk option 
\family typewriter
comment
\family default
.
 Users may define a hook function for the source code like this to use the
 
\family typewriter
lstlisting
\family default
 environment:
\end_layout

\begin_layout Standard
\begin_inset ERT
status open

\begin_layout Plain Layout

<<hook-source, eval=FALSE>>=
\end_layout

\begin_layout Plain Layout

knit_hooks$set(source = function(x, options) {
\end_layout

\begin_layout Plain Layout

paste('
\backslash

\backslash
begin{lstlisting}
\backslash
n', x, '
\backslash

\backslash
end{lstlisting}
\backslash
n', sep = '')
\end_layout

\begin_layout Plain Layout

})
\end_layout

\begin_layout Plain Layout

@
\end_layout

\end_inset


\end_layout

\begin_layout Standard
Similarly we can put other types of output into other environments.
 There is no need to hack at 
\family sans
Sweave.sty
\family default
 for 
\series bold
knitr
\series default
 and you can put the output in any environments.
 What is more, the output hooks make 
\series bold
knitr
\series default
 ready for other types of output, and a typical one is HTML (there are built-in
 hooks).
 The website has provided many examples demonstrating the flexibility of
 the output.
\end_layout

\begin_layout Section
Features
\end_layout

\begin_layout Standard
The 
\series bold
knitr
\series default
 package borrowed features such as tikz graphics and cache from 
\series bold
pgfSweave
\series default
 
\begin_inset CommandInset citation
LatexCommand citep
key "R-pgfSweave"

\end_inset

 and 
\series bold
cacheSweave
\series default
 
\begin_inset CommandInset citation
LatexCommand citep
key "R-cacheSweave"

\end_inset

 respectively, but the implementations are different.
 New features like code reference from an external R script as well as output
 customization are also introduced.
 The feature of hook functions in Sweave is re-implemented and hooks have
 new usage now.
 There are several other small features which are motivated from my everyday
 use of Sweave.
 For example, a progress bar is provided when knitting a file so we roughly
 know how long we still need to wait; output from inline R code (e.g.
 
\family typewriter

\backslash
Sexpr{x[1]}
\family default
) is automatically formatted in TeX math notation (like 
\begin_inset ERT
status collapsed

\begin_layout Plain Layout


\backslash
Sexpr{123456789}
\end_layout

\end_inset

) if the result is numeric, and we will not get too many digits by default.
 You may check out a number of specific manuals dedicated to specific features
 such as graphics in the website: 
\begin_inset Flex URL
status collapsed

\begin_layout Plain Layout

http://yihui.name/knitr/demos
\end_layout

\end_inset

.
\end_layout

\begin_layout Subsection
Code Decoration
\end_layout

\begin_layout Standard
The 
\series bold
highlight
\series default
 package 
\begin_inset CommandInset citation
LatexCommand citep
key "R-highlight"

\end_inset

 is used by default to highlight R code, and 
\series bold
formatR
\series default
 
\begin_inset CommandInset citation
LatexCommand citep
key "R-formatR"

\end_inset

 is used to reformat R code (like 
\family typewriter
keep.source=FALSE
\family default
 in Sweave but will also try to retain comments).
 For LaTeX output, the 
\series bold
framed
\series default
 package is used to decorate code chunks with a light gray background.
 If this LaTeX package is not found in the system, a version will be copied
 directly from 
\series bold
knitr
\series default
.
 The prompt characters are removed by default because they mangle the R
 source code in the output and make it difficult to copy R code.
 The R output is masked in comments by default based on the same rationale.
 It is easy to revert to the output with prompts (set option 
\family typewriter
prompt=TRUE
\family default
), and you will quickly realize the inconvenience to the readers if they
 want to copy and run the code in the output document:
\end_layout

\begin_layout Standard
\begin_inset ERT
status open

\begin_layout Plain Layout

<<stupid-prompts, prompt=TRUE, comment=NA, highlight=FALSE>>=
\end_layout

\begin_layout Plain Layout

x=rnorm(5)
\end_layout

\begin_layout Plain Layout

x
\end_layout

\begin_layout Plain Layout

var(x)
\end_layout

\begin_layout Plain Layout

@
\end_layout

\end_inset


\end_layout

\begin_layout Standard
The example below shows the effect of 
\family typewriter
tidy=TRUE/FALSE
\family default
:
\end_layout

\begin_layout Standard
\begin_inset ERT
status open

\begin_layout Plain Layout

<<tidy-no, eval=FALSE, tidy=FALSE>>=
\end_layout

\begin_layout Plain Layout

## option tidy=FALSE
\end_layout

\begin_layout Plain Layout

for(k in 1:10){j=cos(sin(k)*k^2)+3;print(j-5)}
\end_layout

\begin_layout Plain Layout

@
\end_layout

\begin_layout Plain Layout

<<tidy-yes, eval=FALSE, tidy=TRUE>>=
\end_layout

\begin_layout Plain Layout

## option tidy=TRUE
\end_layout

\begin_layout Plain Layout

for(k in 1:10){j=cos(sin(k)*k^2)+3;print(j-5)}
\end_layout

\begin_layout Plain Layout

@
\end_layout

\end_inset


\end_layout

\begin_layout Standard
Note 
\family typewriter
=
\family default
 is replaced by 
\family typewriter
<-
\family default
 because 
\family typewriter
options('replace.assign')
\family default
 was set to be 
\family typewriter
TRUE
\family default
 in this document; see the documentation of 
\emph on
tidy.source()
\emph default
 in 
\series bold
formatR
\series default
 for details.
\end_layout

\begin_layout Standard
Many highlighting themes can be used in 
\series bold
knitr
\series default
, which are borrowed from the 
\series bold
highlight
\series default
 package by 
\begin_inset CommandInset href
LatexCommand href
name "Andre Simon"
target "http://www.andre-simon.de/"

\end_inset


\begin_inset Foot
status open

\begin_layout Plain Layout
not the R package mentioned before; for a preview of these themes, see 
\begin_inset Flex URL
status collapsed

\begin_layout Plain Layout

http://www.andre-simon.de/dokuwiki/doku.php?id=theme_examples
\end_layout

\end_inset


\end_layout

\end_inset

; it is also possible to use themes from 
\begin_inset Flex URL
status collapsed

\begin_layout Plain Layout

http://www.eclipsecolorthemes.org/
\end_layout

\end_inset

 by providing a theme id to 
\series bold
knitr
\series default

\begin_inset Foot
status open

\begin_layout Plain Layout
many thanks to 
\begin_inset CommandInset href
LatexCommand href
name "Ramnath Vaidyanathan"
target "https://github.com/ramnathv"

\end_inset

 for the work on themes
\end_layout

\end_inset

.
 See 
\family typewriter
?knit_theme
\family default
 for details.
\end_layout

\begin_layout Subsection
Graphics
\end_layout

\begin_layout Standard
Graphics is an important part of reports, and several enhancements have
 been made in 
\series bold
knitr
\series default
.
 For example, grid graphics may not need to be explicitly printed as long
 as the same code can produce plots in R (in some cases, however, they have
 to be printed, e.g.
 in a loop, because you have to do so in an R terminal).
\end_layout

\begin_layout Subsubsection
Graphical Devices
\end_layout

\begin_layout Standard
Over a long time, a frequently requested feature for Sweave was the support
 for other graphics devices, which has been implemented since R 2.13.0.
 Instead of using logical options like 
\family typewriter
png
\family default
 or 
\family typewriter
jpeg
\family default
 (this list can go on and on), 
\series bold
knitr
\series default
 uses a single option 
\family typewriter
dev
\family default
 (like 
\family typewriter
grdevice
\family default
 in Sweave) which has support for more than 20 devices.
 For instance, 
\family typewriter
dev='png'
\family default
 will use the 
\emph on
png()
\emph default
 device, and 
\family typewriter
dev='CairoJPEG'
\family default
 uses the 
\emph on
CairoJPEG()
\emph default
 device in the 
\series bold
Cairo
\series default
 package (it has to be installed first, of course).
 If none of these devices is satisfactory, you can provide the name of a
 customized device function, which must have been defined before it is called.
\end_layout

\begin_layout Subsubsection
Plot Recording
\end_layout

\begin_layout Standard
As mentioned before, all the plots in a code chunk are first recorded as
 R objects and then 
\begin_inset Quotes eld
\end_inset

replayed
\begin_inset Quotes erd
\end_inset

 inside a graphical device to generate plot files.
 The 
\series bold
evaluate
\series default
 package will record plots per 
\emph on
expression
\emph default
 basis, in other words, the source code is split into individual complete
 expressions and 
\series bold
evaluate
\series default
 will examine possible plot changes in snapshots after each single expression
 has been evaluated.
 For example, the code below consists of three expressions, out of which
 two are related to drawing plots, therefore 
\series bold
evaluate
\series default
 will produce two plots by default:
\end_layout

\begin_layout Standard
\begin_inset ERT
status open

\begin_layout Plain Layout

<<low-level-plots, fig.keep='all', dev='tikz', fig.width=2.5, fig.height=2.5,
 out.width='.3
\backslash

\backslash
textwidth', cache=TRUE>>=
\end_layout

\begin_layout Plain Layout

par(mar=c(3,3,.1,.1))
\end_layout

\begin_layout Plain Layout

plot(1:10, ann=FALSE,las=1)
\end_layout

\begin_layout Plain Layout

text(5,9,'mass $
\backslash

\backslash
rightarrow$ energy
\backslash
n$E=mc^2$')
\end_layout

\begin_layout Plain Layout

@
\end_layout

\end_inset


\end_layout

\begin_layout Standard
This brings a significant difference with traditional tools in R for dynamic
 report generation, since low-level plotting changes can also be recorded.
 The option 
\family typewriter
fig.keep
\family default
 controls which plots to keep in the output; 
\family typewriter
fig.keep='all'
\family default
 will keep low-level changes as separate plots; by default (
\family typewriter
fig.keep='high'
\family default
), 
\series bold
knitr
\series default
 will merge low-level plot changes into the previous high-level plot, like
 most graphics devices do.
 This feature may be useful for teaching R graphics step by step.
 Note, however, low-level plotting commands in a single expression (a typical
 case is a loop) will not be recorded accumulatively, but high-level plotting
 commands, regardless of where they are, will always be recorded.
 For example, this chunk will only produce 2 plots instead of 21 plots because
 there are 2 complete expressions:
\end_layout

\begin_layout Standard
\begin_inset ERT
status open

\begin_layout Plain Layout

<<low-plot-loop, eval=FALSE>>=
\end_layout

\begin_layout Plain Layout

plot(0,0,type='n',ann=FALSE)
\end_layout

\begin_layout Plain Layout

for(i in seq(0, 2*pi,length=20)) points(cos(i),sin(i))
\end_layout

\begin_layout Plain Layout

@
\end_layout

\end_inset


\end_layout

\begin_layout Standard
But this will produce 20 plots as expected:
\end_layout

\begin_layout Standard
\begin_inset ERT
status open

\begin_layout Plain Layout

<<high-plot-loop, eval=FALSE>>=
\end_layout

\begin_layout Plain Layout

for(i in seq(0, 2*pi,length=20)) {plot(cos(i),sin(i),xlim=c(-1,1),ylim=c(-1,1))}
\end_layout

\begin_layout Plain Layout

@
\end_layout

\end_inset


\end_layout

\begin_layout Standard
As I showed in the beginning of this manual, it is straightforward to let
 
\series bold
knitr
\series default
 keep all the plots in a chunk and insert them into the output document,
 so we no longer need the 
\family typewriter
cat('
\backslash

\backslash
includegraphics{}')
\family default
 trick.
\end_layout

\begin_layout Standard
We can discard all previous plots and keep the last one only by 
\family typewriter
fig.keep='last'
\family default
, or keep only the first plot by 
\family typewriter
fig.keep='first'
\family default
, or discard all plots by 
\family typewriter
fig.keep='none'
\family default
.
\end_layout

\begin_layout Subsubsection
Plot Rearrangement
\end_layout

\begin_layout Standard
The option 
\family typewriter
fig.show
\family default
 can decide whether to hold all plots while evaluating the code and 
\begin_inset Quotes eld
\end_inset

flush
\begin_inset Quotes erd
\end_inset

 all of them to the end of a chunk (
\family typewriter
fig.show='hold'
\family default
), or just insert them to the place where they were created (by default
 
\family typewriter
fig.show='asis'
\family default
).
 Here is an example of 
\family typewriter
fig.show='asis'
\family default
:
\end_layout

\begin_layout Standard
\begin_inset ERT
status open

\begin_layout Plain Layout

<<fig-hold, fig.show='asis', dev='pdf', fig.width=6, fig.height=4, out.width='.35
\backslash

\backslash
linewidth'>>=
\end_layout

\begin_layout Plain Layout

contour(volcano)  # contour lines
\end_layout

\begin_layout Plain Layout

filled.contour(volcano)  # fill contour plot with colors
\end_layout

\begin_layout Plain Layout

@
\end_layout

\end_inset


\end_layout

\begin_layout Standard
Beside 
\family typewriter
hold
\family default
 and 
\family typewriter
asis
\family default
, the option 
\family typewriter
fig.show
\family default
 can take a third value: 
\family typewriter
animate
\family default
, which makes it possible to insert animations into the output document.
 In LaTeX, the package 
\series bold
animate
\series default
 is used to put together image frames as an animation.
 For animations to work, there must be more than one plot produced in a
 chunk.
 The option 
\family typewriter
interval
\family default
 controls the time interval between animation frames; by default it is 1
 second.
 Note you have to add 
\family typewriter

\backslash
usepackage{animate}
\family default
 in the LaTeX preamble, because 
\series bold
knitr
\series default
 will not add it automatically.
 Animations in the PDF output can only be viewed in Adobe Reader.
\end_layout

\begin_layout Standard
As a simple demonstration, here is a 
\begin_inset CommandInset href
LatexCommand href
name "Mandelbrot animation"
target "http://en.wikipedia.org/wiki/Mandelbrot_set"

\end_inset

 taken from the 
\series bold
animation
\series default
 package 
\begin_inset CommandInset citation
LatexCommand citep
key "R-animation"

\end_inset

; note the PNG device is used because PDF files are too large.
 You should be able to see the animation immediately with Acrobat Reader
 since it was set to play automatically:
\end_layout

\begin_layout Standard
\begin_inset ERT
status open

\begin_layout Plain Layout

<<animate-demo, fig.show='animate', dev='png', out.width='.45
\backslash

\backslash
linewidth', interval=.5, aniopts='controls,loop,autoplay',  cache=TRUE>>=
\end_layout

\begin_layout Plain Layout

library(animation)
\end_layout

\begin_layout Plain Layout

demo('Mandelbrot', echo = FALSE, package = 'animation')
\end_layout

\begin_layout Plain Layout

@
\end_layout

\end_inset


\end_layout

\begin_layout Subsubsection
Plot Size
\end_layout

\begin_layout Standard
The 
\family typewriter
fig.width
\family default
 and 
\family typewriter
fig.height
\family default
 options specify the size of plots in the graphics device, and the real
 size in the output document can be different (see 
\family typewriter
out.width
\family default
 and 
\family typewriter
out.height
\family default
).
 When there are multiple plots per chunk, it is possible to arrange more
 than one plot per line in LaTeX -- just specify 
\family typewriter
out.width
\family default
 to be less than half of the current line width, e.g.
 
\family typewriter
out.width='.49
\backslash

\backslash
linewidth'
\family default
.
\end_layout

\begin_layout Subsubsection
The tikz Device
\end_layout

\begin_layout Standard
Beside PDF, PNG and other traditional R graphical devices, 
\series bold
knitr
\series default
 has special support to tikz graphics via the 
\series bold
tikzDevice
\series default
 package 
\begin_inset CommandInset citation
LatexCommand citep
key "R-tikzDevice"

\end_inset

, which is similar to 
\series bold
pgfSweave
\series default
.
 If we set the chunk option 
\family typewriter
dev='tikz'
\family default
, the 
\emph on
tikz()
\emph default
 device in 
\series bold
tikzDevice
\series default
 will be used to record plots.
 Options 
\family typewriter
sanitize
\family default
 and 
\family typewriter
external
\family default
 are related to the tikz device: see the documentation of 
\emph on
tikz()
\emph default
 for details.
 Note 
\family typewriter
external=TRUE
\family default
 in 
\series bold
knitr
\series default
 has a different meaning with 
\series bold
pgfSweave
\series default
 -- it means 
\family typewriter
standAlone=TRUE
\family default
 in 
\emph on
tikz()
\emph default
, and the tikz graphics output will be compiled to PDF 
\emph on
immediately
\emph default
 after it is created, so the 
\begin_inset Quotes eld
\end_inset

externalization
\begin_inset Quotes erd
\end_inset

 does not depend on the 
\series bold
tikz
\series default
 package; to maintain consistency in (font) styles, 
\series bold
knitr
\series default
 will read the preamble of the input document and use it in the tikz device.
 At the moment, I'm not sure if this is a faithful way to externalize tikz
 graphics, but I have not seen any problems so far.
 The assumption to make, however, is that you declare all the styles in
 the preamble; 
\series bold
knitr
\series default
 is agnostic of 
\emph on
local
\emph default
 style changes in the body of the document.
\end_layout

\begin_layout Standard
Below is an example taken from StackOverflow
\begin_inset Foot
status open

\begin_layout Plain Layout
\begin_inset Flex URL
status collapsed

\begin_layout Plain Layout

http://stackoverflow.com/q/8190087/559676
\end_layout

\end_inset


\end_layout

\end_inset

; we usually have to write R code like this to obtain a math expression
 
\begin_inset Formula $\mathrm{d}\mathbf{x}_{t}=\alpha[(\theta-\mathbf{x}_{t})\mathrm{d}t+4]\mathrm{d}B_{t}$
\end_inset

 in R graphics:
\end_layout

\begin_layout Standard
\begin_inset ERT
status open

\begin_layout Plain Layout

<<math-expr-R, eval=FALSE>>=
\end_layout

\begin_layout Plain Layout

qplot(1:10, 1:10) + opts(title = substitute(paste(d * 
\end_layout

\begin_layout Plain Layout

    bolditalic(x)[italic(t)] == alpha * (theta - bolditalic(x)[italic(t)])
 * 
\end_layout

\begin_layout Plain Layout

    d * italic(t) + lambda * d * italic(B)[italic(t)]), list(lambda = 4)))
 
\end_layout

\begin_layout Plain Layout

@
\end_layout

\end_inset


\end_layout

\begin_layout Standard
With the tikz device, it is both straightforward and more beautiful: 
\end_layout

\begin_layout Standard
\begin_inset ERT
status open

\begin_layout Plain Layout

<<math-expr-tikz, dev='tikz', fig.width=5, fig.height=3, out.width='.55
\backslash

\backslash
linewidth', cache=TRUE, message=FALSE>>=
\end_layout

\begin_layout Plain Layout

library(ggplot2)
\end_layout

\begin_layout Plain Layout

qplot(1:10, 1:10) + 
\end_layout

\begin_layout Plain Layout

opts(title = sprintf('$
\backslash

\backslash
mathrm{d}
\backslash

\backslash
mathbf{x}_{t} = 
\backslash

\backslash
alpha[(
\backslash

\backslash
theta - 
\backslash

\backslash
mathbf{x}_{t})
\backslash

\backslash
mathrm{d}t + %d]
\backslash

\backslash
mathrm{d}B_{t}$', 4))
\end_layout

\begin_layout Plain Layout

@
\end_layout

\end_inset


\end_layout

\begin_layout Standard
The advantage of tikz graphics is the consistency of styles
\begin_inset Foot
status collapsed

\begin_layout Plain Layout
Users are encouraged to read the vignette of 
\series bold
tikzDevice
\series default
, which is the most beautiful vignette I have ever seen in R packages: 
\begin_inset Flex URL
status collapsed

\begin_layout Plain Layout

http://cran.r-project.org/web/packages/tikzDevice/vignettes/tikzDevice.pdf
\end_layout

\end_inset


\end_layout

\end_inset

, and one disadvantage is that LaTeX may not be able to handle too large
 tikz files (it can run out of memory).
 For example, an R plot with tens of thousands of graphical elements may
 fail to compile in LaTeX if we use the tikz device.
 In such cases, we can switch to the PDF or PNG device, or reconsider our
 decision on the type of plots, e.g., a scatter plot with millions of points
 is usually difficult to read, and a contour plot or a hexagon plot showing
 the 2D density can be a better alternative (they are smaller in size).
\end_layout

\begin_layout Standard
The graphics manual contains more detailed information and you can check
 it out in the 
\begin_inset CommandInset href
LatexCommand href
name "website"
target "http://yihui.name/knitr/demo/graphics/"

\end_inset

.
\end_layout

\begin_layout Subsection
Cache
\end_layout

\begin_layout Standard
The feature of cache is not a new idea -- both 
\series bold
cacheSweave
\series default
 and 
\series bold
weaver
\series default
 have implemented it based on Sweave, with the former using 
\series bold
filehash
\series default
 and the latter using 
\family sans
.RData
\family default
 images; 
\series bold
cacheSweave
\series default
 also supports lazy-loading of objects based on 
\series bold
filehash
\series default
.
 The 
\series bold
knitr
\series default
 package directly uses internal base R functions to save (
\emph on
tools:::makeLazyLoadDB()
\emph default
) and lazy-load objects (
\emph on
lazyLoad()
\emph default
).
 These functions are either undocumented or marked as internal, but as far
 as I understand, they are the tools to implement lazy-loading for packages.
 The 
\series bold
cacheSweave
\series default
 vignette has clearly explained lazy-loading, and roughly speaking, lazy-loading
 means an object will not be really loaded into memory unless it is really
 used somewhere.
 This is very useful for cache; sometimes we read a large object and cache
 it, then take a subset for analysis and this subset is also cached; in
 the future, the initial large object will not be loaded into R if our computati
on is only based on the object of its subset.
\end_layout

\begin_layout Standard
The paths of cache files are determined by the chunk option 
\family typewriter
cache.path
\family default
; by default all cache files are created under a directory 
\family sans
cache
\family default
 relative to the current working directory, and if the option value contains
 a directory (e.g.
 
\family typewriter
cache.path='cache/abc-'
\family default
), cache files will be stored under that directory (automatically created
 if it does not exist).
 The cache is invalidated and purged on any changes to the code chunk, including
 both the R code and chunk options
\begin_inset Foot
status open

\begin_layout Plain Layout
One exception is the 
\family typewriter
include
\family default
 option, which is not cached because 
\family typewriter
include=TRUE/FALSE
\family default
 does not affect code evaluation; meanwhile, the value 
\family typewriter
getOption('width')
\family default
 is also cached, so if you change this option, the cache will also be invalidate
d (this option affects the width of text output)
\end_layout

\end_inset

; this means previous cache files of this chunk are removed (filenames are
 identified by the chunk label).
 Unlike 
\series bold
pgfSweave
\series default
, cache files will never accumulate since old cache files will always be
 removed in 
\series bold
knitr
\series default
.
 Unlike 
\series bold
weaver
\series default
 or 
\series bold
cacheSweave
\series default
, 
\series bold
knitr
\series default
 will try to preserve these side-effects:
\end_layout

\begin_layout Enumerate
printed results: meaning that any output of a code chunk will be loaded
 into the output document for a cached chunk, although it is not really
 evaluated.
 The reason is 
\series bold
knitr
\series default
 also cache the output of a chunk as a character string.
 Note this means graphics output is also cached since it is part of the
 output.
 It has been a pain for me for a long time to have to lose output to gain
 cache;
\end_layout

\begin_layout Enumerate
loaded packages: after the evaluation of each cached chunk, the list of
 packages used in the current R session is written to a file under the cache
 path named 
\family sans
__packages
\family default
; next time if a cached chunk needs to be rebuilt, these packages will be
 loaded first.
 The reasons for caching package names are, it can be slow to load some
 packages, and a package might be loaded in a previous cached chunk which
 is not available to the next cached chunk when only the latter needs to
 be rebuilt.
 Note this only applies to cached chunks, and for uncached chunks, you must
 always use 
\emph on
library()
\emph default
 to load packages explicitly;
\end_layout

\begin_layout Standard
Although 
\series bold
knitr
\series default
 tries to keep some side-effects, there are still other types of side-effects
 like setting 
\emph on
par()
\emph default
 or 
\emph on
options()
\emph default
 which are not cached.
 Users should be aware of these special cases, and make sure to clearly
 separate the code which is not meant to be cached to other chunks which
 are not cached, e.g., set all global options in the first chunk of a document
 and do not cache that chunk.
\end_layout

\begin_layout Standard
Sometimes a cached chunk may need to use objects from other cached chunks,
 which can bring a serious problem -- if objects in previous chunks have
 changed, this chunk will not be aware of the changes and will still use
 old cached results, unless there is a way to detect such changes from other
 chunks.
 There is an option called 
\family typewriter
dependson
\family default
 in 
\series bold
cacheSweave
\series default
 which does this job.
 We can explicitly specify which other chunks this chunk depends on by setting
 an option like 
\family typewriter
dependson='chunkA;chunkB'
\family default
 or equivalently 
\family typewriter
dependson=c('chunkA', 'chunkB')
\family default
.
 Each time the cache of a chunk is rebuilt, all other chunks which depend
 on this chunk will lose cache, hence their cache will be rebuilt as well.
\end_layout

\begin_layout Standard
Another way to specify the dependencies among chunks is to use the chunk
 option 
\family typewriter
autodep
\family default
 and the function 
\emph on
build_dep()
\emph default
.
 This is an experimental feature borrowed from 
\series bold
weaver
\series default
 which frees us from setting chunk dependencies manually.
 The basic idea is, if a latter chunk uses any objects created from a previous
 chunk, the latter chunk is said to depend on the previous one.
 The function 
\emph on
findGlobals()
\emph default
 in the 
\series bold
codetools
\series default
 package is used to find out all global objects in a chunk, and according
 to its documentation, the result is an approximation.
 Global objects roughly mean the ones which are not created locally, e.g.
 in the expression 
\family typewriter
function() {y <- x}
\family default
, 
\family typewriter
x
\family default
 should be a global object, whereas 
\family typewriter
y
\family default
 is local.
 Meanwhile, we also need to save the list of objects created in each cached
 chunk, so that we can compare them to the global objects in latter chunks.
 For example, if chunk A created an object 
\family typewriter
x
\family default
 and chunk B uses this object, chunk B must depend on A, i.e.
 whenever A changes, B must also be updated.
 When 
\family typewriter
autodep=TRUE
\family default
, 
\series bold
knitr
\series default
 will write out the names of objects created in a cached chunk as well as
 those global objects in two files named 
\family sans
__objects
\family default
 and 
\family sans
__globals
\family default
 respectively; later we can use the function 
\emph on
build_dep()
\emph default
 to analyze the object names to figure out the dependencies automatically.
 See 
\begin_inset Flex URL
status collapsed

\begin_layout Plain Layout

http://yihui.name/knitr/demo/cache/
\end_layout

\end_inset

 for examples.
\end_layout

\begin_layout Subsection
Code Externalization
\end_layout

\begin_layout Standard
It can be more convenient to write R code in a separate file, rather than
 mixing it into a LaTeX document; for example, we can run R code successively
 in a pure R script from one chunk to the other without jumping through
 other texts.
 Since I prefer using LyX to write reports, Sweave is even more inconvenient
 because I have to recompile the whole document each time, even if I only
 want to know the results of a single chunk.
 Therefore 
\series bold
knitr
\series default
 introduced the feature of code externalization to a separate R script.
 Currently the setting is like this: the R script also uses chunk labels
 (marked in the form 
\family typewriter
## @knitr chunk-label
\family default
 by default); if the code chunk in the input document is empty, 
\series bold
knitr
\series default
 will match its label with the label in the R script to input external R
 code.
 For example, suppose this is a code chunk labelled as 
\family typewriter
Q1
\family default
 in an R script named 
\family sans
homework1-xie.R
\family default
 which is under the same directory as the Rnw document:
\end_layout

\begin_layout Standard
\begin_inset ERT
status open

\begin_layout Plain Layout

<<ext-r-code, eval=FALSE>>=
\end_layout

\begin_layout Plain Layout

## @knitr Q1
\end_layout

\begin_layout Plain Layout

gcd = function(m, n) {
\end_layout

\begin_layout Plain Layout

    while ((r <- m %% n) != 0) {
\end_layout

\begin_layout Plain Layout

       m = n; n = r
\end_layout

\begin_layout Plain Layout

    }
\end_layout

\begin_layout Plain Layout

    n
\end_layout

\begin_layout Plain Layout

}
\end_layout

\begin_layout Plain Layout

@
\end_layout

\end_inset


\end_layout

\begin_layout Standard
In the Rnw document, we can first read the script using the function 
\emph on
read_chunk()
\emph default
:
\end_layout

\begin_layout Standard
\begin_inset ERT
status open

\begin_layout Plain Layout

<<read-chunk, eval=FALSE>>=
\end_layout

\begin_layout Plain Layout

read_chunk('homework1-xie.R')
\end_layout

\begin_layout Plain Layout

@
\end_layout

\end_inset


\end_layout

\begin_layout Standard
This is usually done in an early chunk, and we can use the chunk 
\family typewriter
Q1
\family default
 later in the Rnw document:
\end_layout

\begin_layout Standard
\begin_inset ERT
status open

\begin_layout Plain Layout

<<use-ext-chunk, echo=FALSE, comment=NA>>=
\end_layout

\begin_layout Plain Layout

cat('<<Q1, echo=TRUE, tidy=TRUE>>=','@',sep='
\backslash
n')
\end_layout

\begin_layout Plain Layout

@
\end_layout

\end_inset


\end_layout

\begin_layout Standard
Different documents can read the same R script, so the R code can be reusable
 across different input documents.
\end_layout

\begin_layout Subsection
Evaluation of Chunk Options
\begin_inset CommandInset label
LatexCommand label
name "sub:conditional"

\end_inset


\end_layout

\begin_layout Standard
By default 
\series bold
knitr
\series default
 uses a new syntax to parse chunk options: it treats them as function arguments
 instead of a text string to be split to obtain option values.
 This gives the user much more power than the old syntax; we can pass arbitrary
 R objects to chunk options besides simple ones like 
\family typewriter
TRUE
\family default
/
\family typewriter
FALSE
\family default
, numbers and character strings.
 The page 
\begin_inset Flex URL
status collapsed

\begin_layout Plain Layout

http://yihui.name/knitr/demo/sweave/
\end_layout

\end_inset

 has given two examples to show the advantages of the new syntax.
 Here we show yet another useful application.
\end_layout

\begin_layout Standard
Before 
\series bold
knitr
\series default
 0.3, there was a feature named 
\begin_inset Quotes eld
\end_inset

conditional evaluation
\begin_inset Quotes erd
\end_inset


\begin_inset Foot
status open

\begin_layout Plain Layout
request from 
\begin_inset Flex URL
status collapsed

\begin_layout Plain Layout

https://plus.google.com/u/0/116405544829727492615/posts/43WrRUffjzK
\end_layout

\end_inset


\end_layout

\end_inset

.
 The idea is, instead of setting chunk options 
\family typewriter
eval
\family default
 and 
\family typewriter
echo
\family default
 to be 
\family typewriter
TRUE
\family default
 or 
\family typewriter
FALSE
\family default
 (constants), their values can be controlled by global variables in the
 current R session.
 This enables 
\series bold
knitr
\series default
 to conditionally evaluate code chunks according to variables.
 For example, here we assign 
\family typewriter
TRUE
\family default
 to a variable 
\family typewriter
dothis
\family default
:
\end_layout

\begin_layout Standard
\begin_inset ERT
status open

\begin_layout Plain Layout

<<cond-variable>>=
\end_layout

\begin_layout Plain Layout

dothis=TRUE
\end_layout

\begin_layout Plain Layout

@
\end_layout

\end_inset


\end_layout

\begin_layout Standard
In the next chunk, we set chunk options 
\family typewriter
eval=dothis
\family default
 and 
\family typewriter
echo=!dothis
\family default
, both are valid R expressions since the variable 
\family typewriter
dothis
\family default
 exists.
 As we can see, the source code is hidden, but it was indeed evaluated:
\end_layout

\begin_layout Standard
\begin_inset ERT
status open

\begin_layout Plain Layout

<<cond-out1, eval=dothis, echo=!dothis>>=
\end_layout

\begin_layout Plain Layout

print('you cannot see my source because !dothis is FALSE')
\end_layout

\begin_layout Plain Layout

@
\end_layout

\end_inset


\end_layout

\begin_layout Standard
Then we set 
\family typewriter
eval=dothis
\family default
 and 
\family typewriter
echo=dothis
\family default
 for another chunk:
\end_layout

\begin_layout Standard
\begin_inset ERT
status open

\begin_layout Plain Layout

<<cond-out2,eval=dothis,echo=dothis>>=
\end_layout

\begin_layout Plain Layout

dothis
\end_layout

\begin_layout Plain Layout

@
\end_layout

\end_inset


\end_layout

\begin_layout Standard
If we change the value of 
\family typewriter
dothis
\family default
 to 
\family typewriter
FALSE
\family default
, neither of the above chunks will be evaluated any more.
 Therefore we can control many chunks with a single variable, and present
 results selectively.
\end_layout

\begin_layout Standard
This old feature requires 
\series bold
knitr
\series default
 to treat 
\family typewriter
eval
\family default
 and 
\family typewriter
echo
\family default
 specially, and we can easily see that it is no longer necessary with the
 new syntax: 
\family typewriter
eval=dothis
\family default
 will tell R to find the variable 
\family typewriter
dothis
\family default
 automatically just like we call a function 
\family typewriter
foobar(eval = dothis)
\family default
.
 What is more, all options will be evaluated as R expressions unless they
 are already constants which do not need to be evaluated, so this old feature
 has been generalized to all other options naturally.
\end_layout

\begin_layout Subsection
Customization
\end_layout

\begin_layout Standard
The 
\series bold
knitr
\series default
 package is ready for customization.
 Both the patterns and hooks can be customized; see the package website
 for details.
 Here I show an example on how to save 
\series bold
rgl
\series default
 plots 
\begin_inset CommandInset citation
LatexCommand citep
key "R-rgl"

\end_inset

 using a customized hook function.
 First we define a hook named 
\family typewriter
rgl
\family default
 using the function 
\emph on
hook_rgl()
\emph default
 in 
\series bold
knitr
\series default
:
\end_layout

\begin_layout Standard
\begin_inset ERT
status open

\begin_layout Plain Layout

<<rgl-demo>>=
\end_layout

\begin_layout Plain Layout

knit_hooks$set(rgl = hook_rgl)
\end_layout

\begin_layout Plain Layout

head(hook_rgl)  # the hook function is defined as this
\end_layout

\begin_layout Plain Layout

@
\end_layout

\end_inset


\end_layout

\begin_layout Standard
Then we only have to set the chunk option 
\family typewriter
rgl=TRUE
\family default
:
\end_layout

\begin_layout Standard
\begin_inset ERT
status open

\begin_layout Plain Layout

<<fancy-rgl, rgl=TRUE, dev='png', fig.width=5, fig.height=5, out.width='2in',
 message=FALSE, cache=TRUE>>=
\end_layout

\begin_layout Plain Layout

library(rgl)
\end_layout

\begin_layout Plain Layout

demo('bivar', package='rgl', echo=FALSE) 
\end_layout

\begin_layout Plain Layout

par3d(zoom=.7)
\end_layout

\begin_layout Plain Layout

@
\end_layout

\end_inset


\end_layout

\begin_layout Standard
Due to the flexibility of output hooks, 
\series bold
knitr
\series default
 supports several different output formats.
 The implementation is fairly easy, e.g., for LaTeX we put R output in 
\family typewriter
verbatim
\family default
 environments, and in HTML, it is only a matter of putting output in 
\family typewriter
div
\family default
 layers.
 These are simply character string operations.
 Many demos in 
\begin_inset Flex URL
status collapsed

\begin_layout Plain Layout

http://yihui.name/knitr/demos
\end_layout

\end_inset

 show this idea clearly.
 This manual did not cover all the features of 
\series bold
knitr
\series default
, and users are encouraged to thumb through the website to know more possible
 features.
\end_layout

\begin_layout Section
Editors
\end_layout

\begin_layout Standard
You can use any text editors to write the source documents, but some have
 built-in support for 
\series bold
knitr
\series default
.
 Both RStudio (
\begin_inset Flex URL
status collapsed

\begin_layout Plain Layout

http://www.rstudio.org
\end_layout

\end_inset

) and LyX (
\begin_inset Flex URL
status collapsed

\begin_layout Plain Layout

http://www.lyx.org
\end_layout

\end_inset

) have full support for 
\series bold
knitr
\series default
, and you can compile the document to PDF with just one click.
 See 
\begin_inset Flex URL
status collapsed

\begin_layout Plain Layout

http://yihui.name/knitr/demo/rstudio/
\end_layout

\end_inset

 and 
\begin_inset Flex URL
status collapsed

\begin_layout Plain Layout

http://yihui.name/knitr/demo/lyx/
\end_layout

\end_inset

 respectively.
\end_layout

\begin_layout Section*
About This Document
\end_layout

\begin_layout Standard
This manual was written in LyX and compiled with 
\series bold
knitr
\series default
 (version 
\begin_inset ERT
status collapsed

\begin_layout Plain Layout


\backslash
Sexpr{packageVersion('knitr')}
\end_layout

\end_inset

).
 The LyX source and the Rnw document exported from LyX can be found under
 these directories:
\end_layout

\begin_layout Standard
\begin_inset ERT
status open

\begin_layout Plain Layout

<<source-location, eval=FALSE>>=
\end_layout

\begin_layout Plain Layout

system.file('examples', 'knitr-manual.lyx', package='knitr')  # lyx source
\end_layout

\begin_layout Plain Layout

system.file('examples', 'knitr-manual.Rnw', package='knitr')  # Rnw source
\end_layout

\begin_layout Plain Layout

@
\end_layout

\end_inset


\end_layout

\begin_layout Standard
You can use the function 
\emph on
knit()
\emph default
 to knit the Rnw document (remember to put the two 
\family sans
.bib
\family default
 files under the same directory), and you need to make sure all the R packages
 used in this document are installed:
\end_layout

\begin_layout Standard
\begin_inset ERT
status open

\begin_layout Plain Layout

<<required-packages, eval=FALSE>>=
\end_layout

\begin_layout Plain Layout

install.packages(c('animation', 'rgl', 'tikzDevice', 'ggplot2'))
\end_layout

\begin_layout Plain Layout

@
\end_layout

\end_inset


\end_layout

\begin_layout Standard
Feedback and comments on this manual and the package are always welcome.
 Bug reports and feature requests can be sent to 
\begin_inset Flex URL
status collapsed

\begin_layout Plain Layout

https://github.com/yihui/knitr/issues
\end_layout

\end_inset

, and questions can be delivered to the 
\begin_inset CommandInset href
LatexCommand href
name "mailing list"
target "knitr@googlegroups.com"
type "mailto:"

\end_inset

 
\begin_inset Flex URL
status collapsed

\begin_layout Plain Layout

https://groups.google.com/group/knitr
\end_layout

\end_inset

.
\end_layout

\begin_layout Standard
\begin_inset ERT
status open

\begin_layout Plain Layout

% when knitr is updated, this chunk will be updated; why?
\end_layout

\begin_layout Plain Layout

<<auto-bib, version=packageVersion('knitr'), echo=FALSE, cache=TRUE, message=FAL
SE>>=
\end_layout

\begin_layout Plain Layout

# write all packages in the current session to a bib file
\end_layout

\begin_layout Plain Layout

write_bib(c(.packages(), 'cacheSweave', 'evaluate', 'formatR', 'highlight',
 'pgfSweave'), file = 'knitr-packages.bib')
\end_layout

\begin_layout Plain Layout

@
\end_layout

\end_inset


\end_layout

\begin_layout Standard
\begin_inset CommandInset bibtex
LatexCommand bibtex
bibfiles "knitr-manual,knitr-packages"
options "jss"

\end_inset


\end_layout

\end_body
\end_document