How to use LaTeX in ggplot via annotate

Question

so I've had this question for quite a while now and I have not found a solution to this. Whenever I want to label a parameter of interest, such as central tendencies (mean, median etc.), for example, I create a vertical and/or horizontal line and use annotate for the labeling. However, I have not been able to use LaTeX and non-hardcoded values concurrently. A MRE is shown below:

data <- data.frame(stat = rnorm(1000))
plot <- 
    ggplot(data, aes(x = stat)) + 
    geom_histogram(aes(y=..density..), fill="aquamarine", color="black") + 
    geom_density(color="black", size=1) + 
    geom_vline(xintercept = 0, color = "blue", linetype="dashed", size = 1) +
    annotate("text", x=-0.2, y=0.2,
             label=paste0("Mean = ", round(mean(data$stat), 4)),
             angle=90, size=7, color="black")

plot

See figure here: https://i.sstatic.net/QzojQ.png

In the example above, I generate some random normal data, save it to a dataframe and plot it. I add a dashed vertical line corresponding to the mean of the data and then label it via annotate. Note, however, that I explicitly write Mean in the label since the LaTeX operators don't work and random letters are not ideal for me.

A solution I found is by using expression instead of paste0 when labeling as shown below:

data <- data.frame(stat = rnorm(1000))
plot <- 
    ggplot(data, aes(x = stat)) + 
    geom_histogram(aes(y=..density..), fill="aquamarine", color="black") + 
    geom_density(color="black", size=1) + 
    geom_vline(xintercept = 0, color = "blue", linetype="dashed", size = 1) +
    annotate("text", x=-0.25, y=0.2, label = expression(mu ~ "= -0.0403"),
             angle=90, size = 7, color = "black")

plot

See figure here: https://i.sstatic.net/rnW5i.png

This allows us to get the LaTeX characters, such as $\mu$ in our case, to show in the plot. But now the downside is that I have to hardcode the mean value in the expression field. This is not ideal and I don't want to do this. I want to be able to do something as follows but this doesn't work:

annotate("text", x=-0.25, y=0.2,            
         label = expression(mu ~ round(mean(data$stat), 4)),
         angle=90, size = 7, color = "black")

I have not been able to find a solution to this so any help is greatly appreciated.

stefan · Accepted Answer · 2022-11-12 10:26:47Z

1

One option to fix that would be to create your expression as a character string instead of using expression and add parse=TRUE to annotate:

library(ggplot2)
set.seed(123)

data <- data.frame(stat = rnorm(1000))
ggplot(data, aes(x = stat)) +
  geom_histogram(aes(y = after_stat(density)), fill = "aquamarine", color = "black") +
  geom_density(color = "black", size = 1) +
  geom_vline(xintercept = 0, color = "blue", linetype = "dashed", size = 1) +
  annotate("text",
    x = -0.2, y = 0.2,
    label = paste0("mu ==", round(mean(data$stat), 4)),
    angle = 90, size = 7, color = "black", parse = TRUE
  )
#> Warning: Using `size` aesthetic for lines was deprecated in ggplot2 3.4.0.
#> ℹ Please use `linewidth` instead.
#> `stat_bin()` using `bins = 30`. Pick better value with `binwidth`.

answered Nov 12, 2022 at 10:26

stefan

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