how to set width and height of matplotlib images in python Rmd chunks?

[tdhock]

hi thanks very much for this package which is very useful for including python chunks in Rmd documents.
Is there a way to control the height and width of the images produced in the chunks? I would like to make Rmd beamer slides with images from matplotlib which have reduced height, but full slide width (so you can write a few lines of commentary above/below the figure).
The fig.width and fig.height have no effect on the image size, and that is documented as R-specific: https://bookdown.org/yihui/rmarkdown-cookbook/figure-size.html says The size of plots made in R can be controlled by the chunk option fig.width and fig.height (in inches).
Is there another way to control matplotlib figure height and width?
The out.height='25%' chunk option works for proportionally reducing the image size (both height and width), but I would like to reduce the height but maintain full width. is that possible?
Thanks and here is a zip file with MRE as Rmd source code with rendered PDF.
slides.zip

[tdhock]

Also would it be possible to output PNG instead of PDF? Slides with PDF/vector graphics take up a lot of disk space (>10MB) so it would be nice to be able to switch to PNG graphics to reduce slide file size.
Looking at the source code I see an option (reticulate.engine.matplotlib.show) which defaults to a function (eng_python_matplotlib_show) that has plt$savefig() so should I write a custom function here? Is this hook documented anywhere? I did not find any documentation from a web search for "r option reticulate.engine.matplotlib.show"

    hook <- getOption("reticulate.engine.matplotlib.show", eng_python_matplotlib_show)

[jwalton3141]

Is there another way to control matplotlib figure height and width?

You could use the figsize argument of matplotlib's plt.figure() command.

So where you have:

```{python}
plt.plot([1, 2, 3, 4]) 
plt.ylabel('some numbers')
plt.show()
```

replace with, eg.

```{python}
plt.figure(figsize=(6, 2))
plt.plot([1, 2, 3, 4])
plt.ylabel('some numbers')
plt.show()
```

[jwalton3141]

would it be possible to output PNG instead of PDF?

Yes. You can do so using the dev figure option of Rmarkdown, as such:

title: "matplotlib test"
author: "Toby Dylan Hocking"
output: 
  beamer_presentation:
    dev: png 

[tdhock]

Great, thanks for the advice. Going forward for other people who have these kinds of questions, can these tips please be documented in some obvious place? For example,

• https://github.com/rstudio/reticulate#python-in-r-markdown
• https://rstudio.github.io/reticulate/articles/versions.html

For the record I was trying to get this to work with plotnine so the final code I used looks like this,

• dev: png in header
• knitr::opts_chunk$set(dpi=500) in R chunk
• plotnine.options.figure_size = (5, 3) in python chunk to set default fig size, can be overridden for specific figures via p9.theme(figure_size=(4.5,2.5))
• p9.theme(subplots_adjust={"left":0.15, "right":0.75, "bottom":0.2, "top":1}) to adjust borders so axis label and legend do not get cut off.

[t-kalinowski]

The standard knitr chunk options fig.width and fig.height should now work:

```{python}
#| fig.width: 8
#| fig.height: 2
import matplotlib.pyplot as plt
plt.plot([1,2,3,4], [1,4,9,16])
```

[tdhock]

Thanks! I confirm this works with these recent R/package versions

R Under development (unstable) (2023-08-23 r85001 ucrt)
Platform: x86_64-w64-mingw32/x64
Running under: Windows 10 x64 (build 19045)

Matrix products: default


locale:
[1] LC_COLLATE=English_United States.utf8 
[2] LC_CTYPE=English_United States.utf8   
[3] LC_MONETARY=English_United States.utf8
[4] LC_NUMERIC=C                          
[5] LC_TIME=English_United States.utf8    

time zone: America/Phoenix
tzcode source: internal

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

loaded via a namespace (and not attached):
 [1] digest_0.6.33     fastmap_1.1.1     xfun_0.40         Matrix_1.6-1     
 [5] lattice_0.21-8    reticulate_1.34.0 knitr_1.43        htmltools_0.5.6  
 [9] png_0.1-8         rmarkdown_2.24    tinytex_0.46      cli_3.6.1        
[13] grid_4.4.0        withr_2.5.0       compiler_4.4.0    highr_0.10       
[17] rstudioapi_0.15.0 tools_4.4.0       evaluate_0.21     Rcpp_1.0.11      
[21] yaml_2.3.7        jsonlite_1.8.7    rlang_1.1.1