Unpredictable figure size in RMD chunk in code loop - r-markdown

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 the default chunk 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 approach 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 <- resizePlot
resizeHeight <- resizeHeight
res <- knitr::knit_child('resizePlot.rmd', quiet = TRUE)
cat(res, sep = '\n')
}
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)
```
And bingo - it looks perfect!