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rggplot2expressionplotmath

Annotate ggplot plot with a multiline expression with objects?

I would like to make an annotation on my ggplot with two lines, sub- and superscripts, and references to objects.

I've figured out that the annotate() function calls geom_text() which when parse = TRUE can use expressions from plotmath.

If this is my label:

q10 = 1.9
a = 3.9
b = -0.05

lab1 = substitute(atop(paste(Q[10], '=', q10), paste(M[O[2]], '=', a, e^(b*T))), list(q10 = q10 = 1.9, a = 3.9, b = -0.05))

Then it will work with base plot:

plot(1, 1, main = lab1)

enter image description here

But when I try to use it with ggplot() it throws an error:

ggplot(diamonds, aes(carat, price, color = cut)) + 
  geom_point() +
  annotate(geom = 'text', x = 4, y = 5000, label = lab1, parse = TRUE, color = 'blue')

Error: Aesthetics must be either length 1 or the same as the data (1): label, colour

I found questions related to multi-line annotations in ggplot: R ggplot annotated with atop using three values and bgoup

and related to expressions in ggplot: ggplot2 annotation with superscripts

But I can't figure out how to combine the appropriate answers to make a working annotation. Any help from the ggplot2 gurus out there?

Solution

  • To use plotmath with ggplot, you pass it in as a string—parse = TRUE refers to parsing the string. Thus:

    library(ggplot2)

ggplot(diamonds, aes(carat, price, color = cut)) + 
    geom_point() +
    annotate(geom = 'text', x = 4, y = 5000, 
             label = "atop(Q[10] == 1.9,M[O[2]] == 3.9*e^(-0.05*T))", 
             parse = TRUE, color = 'blue')

    If you need to substitute into the string, either use paste or glue::glue.