[knitr] Hooks: Customizable functions to run before/after a code chunk and tweak the output of knitr | /knitr/hooks/

Guest *jamiefolson* @ 2012-05-18 12:21:15 originally posted:

Could you provide an example?   I see the code in hooks-extra, but I'm having trouble getting my own hooks executed.  Could you give an Rnw and required compilation commands for using custom hooks?

Guest *ankit sethi* @ 2012-07-06 09:41:41 originally posted:

 Hi Yihui,
First of all, congratulations for a fabulous package.
I was comparing Sweave with Knitr for documentation purpose and wanted to compare the output of the two simultaneously. So, I want to know if I can set Sweaveoptions  for one chunk and knitr for another in the same .Rnw file. For instance, the R-code using sweave looks like (R-code without background color and in typewriter text) and R-code using knitr looks like(code with background and normal fonts)
Thanks in advance.

Guest *Claas-Thido Pfaff* @ 2012-07-29 13:37:11 originally posted:

He Yihui Thanks for this amazing R package. I'd like to knit my .Rnw files and have some plots in it. I have looked into the .tex output produced by knitr and all the figures are included surrounded by the begin{figure}[htbp] ...end{figure}. I like to draw a frame around the plots with tikz and have defined a node in tikz looking like this.:

tikzstyle{pictureframe} = [rectangle, rounded corners, draw]

I  normally surround my other pictures I include into my .tex and .Rnw files by adding a tikzpicture and a the defined node inside the 'figure' environment looking like this:

614 begin{figure}[htbp]
615    centering
616       begin{tikzpicture}
617          node[pictureframe]{%
618             begin{minipage}{0.9textwidth}%
619                begin{center}
620                   includegraphics[width=.8linewidth]{figure}
622                end{center}
623             end{minipage}
624          };
625       end{tikzpicture}
626    captionbelow{#2}
627    label{envlabel}
628 end{figure}

I would like  my plot figures look as the pictures I include.  So how can I realize this? Can you give me a hand with that?

Best Regards Pfaff.

Guest *Mark80305* @ 2012-09-05 04:12:52 originally posted:

Great Package!
One question: In all of your example PDFs, I notice that the light grey background is shown under the R code AND the plots.
When I use your same Rnw code, only the R code has the light grey background -- how do I extend the light grey background to the plots, too?
 

Guest *Stevie P.* @ 2012-09-21 06:24:30 originally posted:

Hi. I was wondering if you could point me to (or post) some examples which successfully use the envir variable inside a hook. I want to create a hook to do some regex work on a certain chunks output, so I thought it'd be clever to try and extract an output variable from that chunk's environment via envir but it just isn't working... Any thoughts?

Guest *heeb* @ 2012-11-07 22:16:28 originally posted:

Is it possible to make an output chunk hook that will automatically set output chunk options?  For example:

g <- function() cat("hi")  

Instead of:

{r results='asis', echo=FALSE}g()

I would like to be able to type

{r myHook=TRUE}g()and by nature of myHook, have the other options automatically specified (echo=FALSE, results='asis'). As far as I understand, I can retrieve the options in the hook function, but I do not know how to set them.

Guest *JoAnn Alvarez* @ 2012-12-05 21:47:55 originally posted:

Can errors and warnings be written to the terminal, and not in the output document or a separate file? Like in Sweave?

hook_log = function(x, options) cat(x, file='messages.txt', append=TRUE)
knit_hooks$set(warning = hook_log, message = hook_log)

Guest *Andrey Chetverikov* @ 2013-01-10 19:36:41 originally posted:

In case if anyone will look for it, here is a hook that removes all Latex comments from output:
knit_hooks$set(document = function(x, options) gsub("%.*n", '', x,perl=T))

I find it useful when working with mtable function that outputs unnecessary comments.

Guest *Rod Alence* @ 2013-02-03 12:20:11 originally posted:

In my lecture slides (Sweave and beamer, with fancyvrb), I use different colors for source (Sinput) and output (Soutput), with something in my preamble like this:
DefineVerbatimEnvironment{Sinput}{Verbatim}{formatcom=color{Blue3}}
DefineVerbatimEnvironment{Sounput}{Verbatim}{formatcom=color{gray}}

I've been able to convert this to knitr successfully using render_sweave(), but I'm wondering (after a few failed attempts) if there's an easy way to do the same thing using output hooks in knitr?

Guest *Remko Duursma* @ 2013-04-02 00:06:58 originally posted:

I found a problem with the prettifying of formulas, when the formula is only one-sided as in xtabs:

xtabs(～ xvar, data=dat)

makes latex,

hlfunctioncall{xtabs}(～dat, data = dat)

Notice the missing space between the ~ and dat! This causes a problem for me, because I used the very nice solution to replace the somewhat ugly default tilde in source code with a nicer, centered one (http://stackoverflow.com/questions/14710477/pretty-tilde-from-r-chunk-with-knitr). When replacing all tildes, the missing space causes havoc!

Thanks for your help.

Guest *Jon* @ 2013-11-06 20:14:37 originally posted:

I am knitting a bunch of R chunks together into an html file. Two chunks are adding calls to jquery resources and I need to remove the duplicate, using a hook. Do you have an example piece of code that does something similar that I might be able to reference?

Guest *Daniel Cher* @ 2014-04-16 00:20:33 originally posted:

Yihui, congratulations on knitr. It's very cool.

I am trying to use knit_hooks to add the following before:

begin{table}[H]
centering
caption{My table caption}

.... then a table generated in R

then after the chunk:

end{table}

I'm using the following:

knit_hooks$set(myTable = function(before, options, envir) {
if (before) {

code to be run before a chunk

str="begin{table}[H]n {centering}n caption{My caption}n"
return(str)
} else {

code to be run after a chunk

return("end{table}n")
}
})

However, I'm seeing "begin{kframe}" and "end{kframe}", which messes things up. I'm not sure how to get rid of these phrases.

One more thing: This removes all "kframe"... and now it works. But the approach seems wrong.

knit_hooks$set(document = function(x) {
gsub('(begin|end){kframe}', '', x)
})

Guest *isomorphisms* @ 2015-02-04 20:57:46 originally posted:

foo_hook = function(before, options, envir) {

In this line, I guess foo is supposed to be replaced with something. (What?) But before, options, envir and are supposed to be written literally as they are? (Because that's the exact word that's already been defined for knitr to look for before knitting.)

Guest *Fábio Salles* @ 2015-12-02 12:10:27 originally posted:

Hi Yihui,

I´m creating a dynamic documet using Rmarkdown/Knitr with many attached figures and tables along different chapters and sections and using package kfigr to citate inline figures/tables resulted from chunks.

I´m facing problems on getting the track of the hierarchical numbering following the chapters/section sequence. The inline output numbering sequence is not following the desired 2 levels (first level for the chapter sequence and second for the figure/table sequence inside that chapter) although the figure/table captions are following the right and desired hierarchical numbering.

How can I fix/set this by calling inline r figr(label, prefix, link, type) or another easy way?

Thanks,

Fabio

Guest *Eduardo W. Ferreira* @ 2016-08-23 19:39:08 originally posted:

Hi Yihui!

Firstly, congratulations for the great work with knitr.

I have a quick question, which I hope can also help others: is there any chunk option to center pander tables? If not, I would love to have some option similarly that for centering plots (set chunk option fig.align='center').

All the best,

Eduardo

Guest *Jerad Acosta* @ 2017-02-10 17:11:29 originally posted:

I LOVE knitr! Thank you for your continued maintenance and further development of this project. I was stoked on R Notebooks (still am) but hope that render_jekyll() output hook will take better fit the majority of my use cases.

Guest *Hamuntu* @ 2017-03-22 13:33:02 originally posted:

Hello,

Joining the happy knitr crew to thank you for these great tools, and also add a quick question: I'm looking for a way to produce a rotated long table in LaTeX from markdown input. I believe output hooks can provide a solution, but could not figure it out ! I would like the chunk output in LaTeX format (longtable environment) to be encapsulated into a landscape environment. Is there a simple way to that please ? The table is produced by a call to pander with chunk option ' results="asis" '. Thanks for your help !!

Guest *Gjalt-Jorn Peters* @ 2019-06-19 16:52:20 originally posted:

The option hooks seem to work a bit differently for the caption, is that possible?

I define a hook for fig.cap that prepends a text. When I verify this using:

> knitr::knit_hooks$get('fig.cap')(list(fig.cap="caption text"))
$fig.cap
[1] "Figure 5: caption text"

It works (yes, it's a figure counter - yes, bookdown does that - but I need custom and deviating text/patterns in the counter prefix).

But when I knit, the hook doesn't seem to be executed. Does this work differently for caption?

(Also: thank you for knitr!!! It is an amazing package that I use quite intensively. Especially now I don't have to continue learning Latex any more (except when exporting to PDFs, but still, much more doable than in the old days. So thank you!!!)

Guest *Michel Ballings* @ 2020-01-26 00:26:03 originally posted:

Hi Yihui, I am trying to apply the following hook https://bookdown.org/yihui/rmarkdown-cookbook/hook-hide.html
on a python chunk using reticulate.
<< engine='python'>>=
a = True # SECRET!!
@
It doesn't hide it. It seems to be working on R chunks only. Any ideas on how to make this work on python chunks?