How to place legend inside caption area on R

Question

I am using R studio / R Markdown to create plots, some with ggplot, some with base R function. I would like to insert a caption for each of my plots which contains the legend similar to the example shown here:

Can anyone suggest how to place the legend of my plots (built with ggplot and base R functions) within the caption as shown in this example?

I searched online and found out that it is possible to use something like:

p +  labs(caption="Figure S1: This is the Figure Legend") 

however, I could not find how to embed the legend into the caption, and I also could not find a solution for plots made using base R.

There are some solutions that require Latex, but I cannot use Latex for this project.

Answer 1

You could just push the legend to the bottom and add a custom title - inlcude a counter to get numbered Plots:

library(ggplot2)
# using the internal iris dataset
iris
# set counter to zero
NR <- 0

# Add counter and build plot
NR <- NR + 1
legend <- paste0("Fig. ", NR, ": This is a Plot about...:")
ggplot2::ggplot(iris, aes(Sepal.Length, Petal.Width, color = Species)) +
  ggplot2::geom_point() +
  ggplot2::labs(color= legend) +
  ggplot2::theme(legend.position = "bottom")


# Add counter and build second plot
NR <- NR + 1
legend <- paste0("Fig. ", NR , ": This is a Plot about...:")
ggplot2::ggplot(iris, aes(Sepal.Width, Petal.Length, color = Species)) +
  ggplot2::geom_point() +
  ggplot2::labs(color= legend) +
  ggplot2::theme(legend.position = "bottom")