extract R code from template using knit_expand()

Question

I have produced a dynamic document using knitr. The document makes extensive use of the package's knit_expand() function for templates. This is illustrated by the MWE (based on Yihui Xie's own example for the function).

• Main document knit-expand-MWE.Rnw

  \documentclass{article}
  
  \title{How to extract code when using\\
  knit\_expand() for templates?}%
  \author{Knitr User}
  
  \begin{document}
  
  \maketitle
  \tableofcontents
  
  \newpage
  \section{Write one row of data}
  
  Only the first two sections are evaluated.
  
  <<run-all, include=FALSE>>=
  library(knitr)
  src = NULL
  for (i in 1:3) src = c(src, knit_expand('template.Rnw'))
  @
  
  \Sexpr{paste(knit(text = src), collapse = '\n')}
  
  \end{document}
  

• Template template.Rnw called by main document

  \subsection{Now i is {{i}}}
  
  This chunk is {{if (i > 2) 'not '}}evaluated.
  <<row-{{i}}, eval={{i <= 2}}>>=
  # row number {{i}}
  iris[{{i}}, ]
  @
  

I now need to extract the corresponding R code. Running purl("knit-expand-MWE.Rnw") outputs knit-expand-MWE.R, which includes the code in the chunk with a reference to the template:

## ----run-all, include=FALSE----------------------------------------------
library(knitr)
src = NULL
for (i in 1:3) src = c(src, knit_expand('template.Rnw'))

What I would like instead is the corresponding "expanded" code (for the benefit of colleagues who do not use knitr), for example:

## ----row-1, eval=TRUE----------------------------------------------
## row number 1
iris[1, ]

## ----row-2, eval=TRUE----------------------------------------------
## row number 2
iris[2, ]

## ----row-3, eval=FALSE----------------------------------------------
## row number 3
iris[3, ]

How can I achieve this?

Answer 1

You can run purl() on src, e. g.

purl(text = src, output = 'knit-expand.R')