Customize Figure Paths In Knitr: A Feature Request

Customizing Figure Paths in Knitr: A Feature Request

Hey guys! I'm here to talk about something that's been bugging me (and maybe you too) for a while now: controlling the file names of figures generated by knitr in R Markdown documents. I've been using knitr for over a decade, and it's been a lifesaver for creating reports and presentations. However, when it comes to managing the output figure file names, I've always felt like there was room for improvement. So, I'm putting in a feature request to allow for custom figure paths, making it easier to organize and reuse those beautiful plots we all create.

The Current State of Affairs: A Quick Recap

Let's quickly recap how knitr handles figures currently. You've got your R Markdown document, you create a code chunk, and you generate a plot. knitr then automatically saves that plot to a file, usually in a figures directory, with a file name based on the chunk label. For instance, if your chunk label is my-awesome-plot, the image might be saved as figures/my-awesome-plot-1.png. This works great, but what if you want more control? What if you want to name your files in a way that makes more sense for your project or allows for easier reuse?

Knitr provides options such as fig.path and dev that you can control, along with the chunk's label: to specify the graphical device and the file path prefix. The chunk label is a significant part of the file name. However, in many cases, the automatically generated names aren't ideal. They might not be descriptive enough, or they might not fit with your overall file naming conventions. This can make it tricky to find specific figures later on, especially when you have many plots scattered throughout your document. I was trying to change the file path, but unfortunately, there isn't a simple way to customize those figure paths and file names.

The Problem: When Default Isn't Enough

The real issue arises when you need more flexibility. Imagine you're generating multiple plots within a single chunk, or you want to reuse the same figure in different contexts. Maybe you're building a presentation where the figures need specific file names. Or perhaps you're using a workflow management tool like Snakemake, where you need to declare specific figures as outputs. In these scenarios, the default knitr file naming becomes a limitation.

For example, suppose you are creating a report with lots of plots for different datasets. If you're looping through datasets and generating plots, you'll end up with a bunch of figures with names like hist-iris-sepal-width-1.png, and it's a bit of a pain to look through them.

As you can see, I am trying to use many different techniques to change the file names, but they don't seem to work, and it's hard to find a perfect way to do so. In this scenario, it is much easier to save it manually and include it explicitly, which adds a whole lot of boilerplate code to each and every code chunk creating plots.

The Proposed Solution: Customization is Key

My suggestion is simple: introduce a new chunk option (perhaps fig.basename or fig.stem) that lets you customize the figure file name. This option could:

• Default to the chunk label for backward compatibility.
• Accept character vectors, recycling or truncating if the length doesn't match the number of figures.
• Accept a function that returns a single character string. This function would have access to local variables, enabling dynamic file name generation based on the current state (e.g., within a loop).

With this change, you could create much more descriptive and organized file names. You'd have more control over the figures in your report and improve the organization. This flexibility is particularly valuable in complex projects where proper organization is essential.

Benefits of this Approach

• Enhanced Organization: Custom file names would make it much easier to locate and identify specific figures. It is much easier to reuse the latest version of a figure.
• Improved Reusability: You could use figures generated in your R Markdown documents in presentations, reports, and other documents.
• Better Integration: This would integrate well with workflow tools like Snakemake.
• Increased Flexibility: Allows users to dynamically generate file names based on the data or context.

Potential Side Effects and Considerations

I believe this could be implemented in a way that's fully backwards compatible. The default behavior would remain unchanged. Only users who specifically use the new chunk option would see any differences. I've thought about it, but there might be edge cases or side effects I haven't considered. I'd love to hear your thoughts on this!

Conclusion: Let's Make knitr Even Better!

This feature request is about giving users more control over their figure file names, which will ultimately enhance the organization, reusability, and integration of knitr plots. With this, we would make knitr even better. Thanks for considering my proposal and for your hard work in maintaining this fantastic tool.