R Knitr: Possible to Programmatically Modify Chunk Labels

R knitr: Possible to programmatically modify chunk labels?

For anyone else who comes across this post, I wanted to point out that @Yihui has provided a formal solution to this question in knitr 1.0 with the introduction of the knit_expand() function. It works great and has really simplified my workflow.

For example, the following will process the template script below for every level of mtcars$cyl, each time replacing all instances of {{ncyl}} (in the template) with its current value:

# My report

```{r}
data(mtcars)
cyl.levels <- unique(mtcars$cyl)
```

## Generate report for each level of cylinder variable
```{r, include=FALSE}
src <- lapply(cyl.levels, function(ncyl) knit_expand(file = "template.Rmd"))
```

`r knit(text = unlist(src))`

Template:

```{r, results='asis'}
cat("### {{ncyl}} cylinders")
```

```{r mpg-histogram-{{ncyl}}cyl}
hist(mtcars$mpg[mtcars$cyl == {{ncyl}}], 
  main = paste({{ncyl}}, "cylinders"))
```

```{r weight-histogam-{{ncyl}}cyl}
hist(mtcars$wt[mtcars$cyl == {{ncyl}}], 
  main = paste({{ncyl}}, "cylinders"))
```

set chunk options on basis of chunk contents

I tend to agree with @user2554330 that you may want to cache the function myFun() instead of code chunks (e.g., with memoise).

Anyway, to answer your question: yes, it is possible to set cache = TRUE with an option hook, e.g.,

knitr::opts_hooks$set(cache = function(options) {
  if (any(grepl('myFun(', options$code))) {
    options$cache <- TRUE
  }
  options
})

grepl() is not an entirely robust way to check if the code chunk contains a call to myFun(). If you want a most robust way, you may try utils::getParseData().

Reuse R child Rmd files - error: duplicate chunk labels

If found a solution:

load("logfile1.Rda")
z <- 1

src <- lapply(z, function(z) knitr::knit_expand(file = "child1.Rmd"))

r knitr::knit(text = unlist(src))

src <- lapply(z, function(z) knitr::knit_expand(file = "child2.Rmd"))

r knitr::knit(text = unlist(src))

load("logfile2.Rda")
z <- 1

src <- lapply(z, function(z) knitr::knit_expand(file = "child1.Rmd"))

r knitr::knit(text = unlist(src))

src <- lapply(z, function(z) knitr::knit_expand(file = "child2.Rmd"))

r knitr::knit(text = unlist(src))

Within the child-files I added {{z}} to each chunk label.

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