Making ggplots Persistent: Save as .rds in R Markdown

Discover how to effortlessly save ggplots from your R Markdown documents as .rds files — a simple guide for effective plotting.

How to Save ggplots as .rds in R Markdown

Saving ggplots as .rds files in R Markdown can sound tricky, but it’s actually a breeze. Let me walk you through a few steps that’ll make your plotting life a whole lot easier.

So, you’re using R Markdown for your data analysis, right? And you’re creating tons of awesome plots using ggplot. But here’s a thing: sometimes you need to save these plots in a way that lets you easily use them later, without rerunning all your code.

Here’s a common scenario: You’ve got your R Markdown document, and you’re generating plots left and right. But, what if you want to combine these plots later, or tweak them without going through the whole analysis again? That’s where saving them as .rds files comes into play. It’s a smart move to keep your plots handy and malleable.

# Example of a basic plot in R Markdown
library(ggplot2)
ggplot(data = iris, aes(x = Sepal.Width, y = Sepal.Length)) + geom_point()

Alright, so how do we save these ggplots? It’s simpler than you think. We’ll use the knit_print function from knitr. This function gives us control over how R objects are printed in R Markdown. So, what we do is set up a knit_print.ggplot method for ggplot objects.

# Setting up knit_print for ggplot
library(knitr)
library(ggplot2)
knit_print.ggplot <- function(x, ...) {
    plotnum <<- plotnum + 1
    saveRDS(x, paste0("plot-", plotnum, ".rds"))
    print(x)
}

With this method, every time you print a ggplot in your R Markdown, it’ll automatically save a .rds file of the plot. This is super handy for keeping track of all your plots without extra hassle.

But wait, there’s more! We can make this even better. Instead of saving just the last plot in a chunk, we can tweak our function to save every plot in a chunk. This means no plot gets left behind!

Here’s how we can modify our function to save every plot in a chunk. We’ll use a counter to keep track of the number of plots in each chunk. This way, we can uniquely name each .rds file based on the plot number. Check out this tweaked version:

# Improved knit_print for saving every plot
knit_print.ggplot <- function(x, ...) {
    if(!exists("plotnum")) plotnum <<- 0
    plotnum <<- plotnum + 1
    saveRDS(x, paste0("chunk-plot-", plotnum, ".rds"))
    print(x)
}

Now, each plot you make in your R Markdown will be saved as a unique .rds file. Whether it’s the first, second, or tenth plot in a chunk, each one gets its own file. This makes reusing and rearranging your plots super easy, giving you more freedom to be creative with your data visualizations.

FAQs and References

Got more questions about saving ggplots in R Markdown as .rds files? I’ve got answers! Plus, check out these official docs for more in-depth info.

FAQs

Q: What’s the easiest way to start with ggplot2?

A: Just begin with ggplot(), add your data and aesthetic mappings with aes(), and layer up with things like geom_point() or geom_histogram()! It's all about layering and customizing your plot.

Q: Can I customize how objects are printed in R Markdown?

A: Absolutely! Use the knit_print function in knitr to tailor how R objects, like plots, are displayed in your document.

Q: Why would I save ggplots as .rds files?

A: Saving plots as .rds files lets you easily reuse and adjust them later without rerunning your entire analysis. It’s a huge time-saver!

References

knitr knit_print function — RDocumentation

ggplot2 — RDocumentation

Originally published on HackingWithCode.com.