How to use superscript in geom_text? - r

Question

I am trying to use superscript in geom_text. But I am unable to do that. I am using the following code
library(caret)
library(tidyverse)
summ <- iris %>%
group_by(Species) %>%
summarise(R = cor(Sepal.Length, Petal.Length, use="pairwise.complete.obs"),
RMSE = RMSE(Sepal.Length, Petal.Length)) %>%
mutate_if(is.numeric, round, digits=2)
p <- ggplot(data=iris, aes(x = Sepal.Length, y = Petal.Length)) +
geom_point(color="blue",alpha = 1/3) +
facet_wrap(Species ~ ., scales="free") +
geom_smooth(method=lm, fill="black", formula = y ~ x) +
xlab("Sepal Length") +
ylab("Petal Length") + theme_bw() +
theme(panel.grid.major = element_blank(), panel.grid.minor = element_blank())
# Here we create our annotations data frame.
df.annotations <- data.frame()
# R
df.annotations <- rbind(df.annotations,
cbind(as.character(summ$Species),
paste("R", summ$R,
sep = " = ")))
# RMSE
df.annotations <- rbind(df.annotations,
cbind(as.character(summ$Species),
paste("RMSE", summ$RMSE,
sep = " = ")))
# This here is important, especially naming the first column
# Species
colnames(df.annotations) <- c("Species", "label")
vertical_adjustment = ifelse(grepl("\\bR\\b",df.annotations$label), 1.5, 3)
p + geom_text(data = df.annotations, aes(x=-Inf, y=+Inf, label=label),
hjust = -0.1, vjust = vertical_adjustment, size=3.5)
My expected output is
How can I add the unit for RMSE after the value and superscript 2 after R i.e. R^2? You can also see that there is a slight shift in the alignment of RMSE with respect to R. How can I make them into the same line?

Answer 1

This could be achieved like so:
Set parse=TRUE in geom_text
Make use of ?plotmath to add superscripts to your labels
# Here we create our annotations data frame.
df.annotations <- data.frame(
Species = rep(summ$Species, 2),
label = c(
paste0("~R^{2} == ", summ$R),
paste0("~RMSE == ", summ$RMSE, "~m^{3} ~m^{-3}")
)
)
vertical_adjustment = ifelse(grepl("\\bR\\b", df.annotations$label), 1.5, 3)
p + geom_text(data = df.annotations, aes(x=-Inf, y=+Inf, label=label),
hjust = 0, vjust = vertical_adjustment, size=3.5, parse = TRUE)

Answer 2

Another approach is to use the ggtext package, which enables markdown formatting in ggplot text objects. I find this syntax much easier to use than R's plotmath, especially for things like italics and color:
df.annotations <- data.frame(
Species = rep(summ$Species, 2),
label = c(
paste0("R<sup>2</sup> = ", summ$R),
paste0("RMSE = ", summ$RMSE, "m<sup>3</sup> m<sup>-3</sup>")
)
)
vertical_adjustment = ifelse(grepl("\\bR\\b", df.annotations$label), 1.5, 2.5)
p + geom_richtext(data = df.annotations, aes(x=-Inf, y=+Inf, label=label),
hjust = 0, vjust = vertical_adjustment, size=3.5, label.size = 0)