Unpredictable figure size in RMD chunk in code loop

Question

I have an rmd chunk of r code with a loop. The structure of the code is like this:

```{r  echo=FALSE, results="asis", out.width="100%"}
  ## out.width="100%"
  ## fig.width=12
  ## fig.height=(6+2*ceiling(6/4))

  section_number <- 3

  i = 1 ## for testing
  while (i <= length(target_var_list)) {
    
    target_var       <- target_var_list[i]
    data_segments    <- data_segments(wrangled_devices, target_var)
    
    # Code  
    exposure_chart_data <- monkeyr::get_exposure_chart_data(wrangled_obs, wrangled_devices, target_var)
    exposure_plot       <- monkeyr::get_exposure_plot(exposure_chart_data, target_var)
    
    # knitr::opts_chunk$set(fig.height=(6+2*ceiling(data_segments/4)))
    print(exposure_plot)
    
    # print(exposure_plot, fig.height=(12+2*ceiling(data_segments/4)))
    
    section_number <- section_number + 1
    cat("\n\n\n")
    i <- i + 1
  }
```

I have commented out a few attempts I made to control the width and height of the plot. And I have commented out 2 attempts I made to control the knitr behaviour on a per plot basis.

The problem is that I can't find a reliable way to control the plot size that accommodates different lengths of the target_var_length.

It is possible to control the height at chunk level, but that is then fixed, and won't respond to each element in the loop. Here are some viz. What I would like is for the actual bar to be the same size in every case. So the case with 3 values would be 75% as wide as the 4. And the case with 7 would look be 2 rows, so twice the height of the 4. Do you see what I mean...

Answer 1

After quite a few hours of messing around with different approaches, here are some insights and an answer.

---

knitr::opts_chunk$set

I expected this to take effect on execution and change the chunk options for whatever elements follow. To change the plot height based on the number of rows / column in a facetted plot, I tried this:

knitr::opts_chunk$set(fig.height=(6+2*ceiling(data_segments/4)))

However it has no effect. The documentation bears this out. This actually sets thedefaultchunk settings for subsequent chunks, and has no effect whatsoever on the current chunk. I encountered another function:

knitr::opts_current$set(fig.height=(6+2*ceiling(data_segments/4)))

The documentation as much as warns you off using this. And I found that it didn't achieve the expected results either in any case.

Blind Hope

I considered the possibility that I was overthinking this and left it up to blind hope by removing all efforts to control the height. Sometimes things just work out you know! ... They didn't.

** Using an rmd child chunk **

This is the appraoch that I finally got to work. It's a slightly horrible hack. My first effort was to create a separate rmd file for each plot:

 ```{r  echo=FALSE, results="asis", out.width="100%", fig.height=(6+2*ceiling(data_segments/4))}
    print(myPlot)
_```  

But that meant creating lots of new rmd plots. I have a major problem with how messy that would get. So I cleaned it up by using a single rmd file for any plot and lumped the code to call it into a fucntion.

resize_plot <- function(resizePlot, resizeHeight) {
    resizePlot <- exposure_plot
    resizeHeight <- 3.25*ceiling(data_segments/4)
    res <- knitr::knit_child('resizePlot.rmd', quiet = TRUE)
    cat(res, sep = '
')
}

Now to insert a custom height plot I just call my new function:

resize_plot(exposure_plot, 3.25*ceiling(data_segments/4))

And the single rmd file just looks like this:

 ```{r  echo=FALSE, results="asis", out.width="100%", fig.height=resizeHeight}

print(resizePlot)