Rmarkdown Chunk Name from Variable - r

Question

How can I use a variable as the chunk name? I have a child document which gets called a number of times, and I need to advance the chunk labels in such a manner than I can also cross reference them.
Something like this:
child.Rmd
```{r }
if(!exists('existing')) existing <- 0
existing = existing + 1
myChunk <- sprintf("myChunk-%s",existing)
```
## Analysis Routine `r existing`
```{r myChunk,echo = FALSE}
#DO SOMETHING, LIKE PLOT
```
master.Rmd
# Analysis Routines
Analysis for this can be seen in figures \ref{myChunk-1}, \ref{myChunk-2} and \ref{myChunk-3}
```{r child = 'child.Rmd'}
```
```{r child = 'child.Rmd'}
```
```{r child = 'child.Rmd'}
```
EDIT POTENTIAL SOLUTION
Here is one potential workaround, inspired by SQL injection of all things...
child.Rmd
```{r }
if(!exists('existing')) existing <- 0
existing = existing + 1
myChunk <- sprintf("myChunk-%s",existing)
```
## Analysis Routine `r existing`
```{r myChunk,echo = FALSE,fig.cap=sprintf("The Caption}\\label{%s",myChunk)}
#DO SOMETHING, LIKE PLOT
```

Answer 1

A suggestion to preknit the Rmd file into another Rmd file before knitting&rendering as follows
master.Rmd:
# Analysis Routines
Analysis for this can be seen in figures `r paste(paste0("\\ref{", CHUNK_NAME, 1:NUM_CHUNKS, "}"), collapse=", ")`
###
rmdTxt <- unlist(lapply(1:NUM_CHUNKS, function(n) {
c(paste0("## Analysis Routine ", n),
paste0("```{r ",CHUNK_NAME, n, ", child = 'child.Rmd'}"),
"```")
}))
writeLines(rmdTxt)
###
child.Rmd:
```{r,echo = FALSE}
plot(rnorm(100))
```
To knit & render the Rmd:
devtools::install_github("chinsoon12/PreKnitPostHTMLRender")
library(PreKnitPostHTMLRender) #requires version >= 0.1.1
NUM_CHUNKS <- 5
CHUNK_NAME <- "myChunk-"
preknit_knit_render_postrender("master.Rmd", "test__test.html")
Hope it helps. Cheers!

Answer 2

If you're getting to this level of complexity, I suggest you look at the brew package.
That provides a templating engine where you can dynamically create the Rmd for knitting.
You get to reference R variables in the outer brew environment, and build you dynamic Rmd from there.

Answer 3

Dynamic chunk names are possible with knitr::knit_expand(). Arguments are referenced in the child document, including in the chunk headers, using {{arg_name}}.
So my parent doc contains:
```{r child_include, results = "asis"}
###
# Generate a section for each dataset
###
species <- c("a", "b")
out <- lapply(species, function(sp) knitr::knit_expand("child.Rmd"))
res = knitr::knit_child(text = unlist(out), quiet = TRUE)
cat(res, sep = "\n")
```
And my child doc, which has no YAML header, contains:
# EDA for species {{sp}}
```{r getname-{{sp}}}
paste("The species is", "{{sp}}")
```
See here in the RMarkdown cookbook.