ggplot format italic annotation

Question

Can I use markup in a ggplot annotation?

Let's say, I have this graph:

p <- function(i) 8*i
a <- function(i) 1+4*i*(i-1)

library(ggplot2)
library(reshape2)

i <- 1:(8*365/7)
d <- data.frame(i=i,p=p(i),a=sapply(i,a))
d <- melt(d, id.vars='i')
p <- ggplot(d, aes(i, value, linetype=variable)) +
    geom_hline(yintercept=700^2) +
    geom_line() +
    scale_linetype_manual(values=c(2,1)) +
    #geom_point() +
    scale_x_continuous(breaks=(0:20)*365/7, labels=0:20) +
    #scale_y_continuous(breaks=c(0,700^2), labels=c(0,expression(L^2)))
    scale_y_sqrt() +
    #scale_y_log10() +
    annotate('text', 8*365/7, 1e3, label="P(i)=8i", hjust=1, size=3) +
    annotate('text', 8*365/7, 2.5e5, label="A(i)=1+4i(i-1)", hjust=1, size=3)
print(p + theme_classic())

output

I know I can use fontface=3 and put everything in italic. But I do not want the numbers in italic, only the variable i. Preferably, P and A would not be in italic as well.

Any ideas?

pbnelson · Answer 1 · 2016-10-26T15:51:57.543

28

Right now this page is the top search result on google for ggplot annotate italic. For the benefit of those who simply want to italicize an entire annotation, I'm writing this post. Use annotate's fontface option. Example:

seq(0,3.14,0.01)
qplot(x, sin(x)) +   # works the same for qplot or ggplot
annotate(geom = 'text', 
         x = 1.5, 
         y = 0.5, 
         hjust = 0.5,
         label = 'Hello, World', 
         fontface = 'italic')

edited Oct 26 '16 at 15:51

answered Oct 26 '16 at 15:31

pbnelson

1,649
16
14

1

FYI, the fontface argument also works with `geom_text` – pbnelson Oct 25 '17 at 14:56

score 23 · Accepted Answer · answered Jun 16 '15 at 14:15

Use parse=TRUE and supply a string formatted according to ?plotmath.

p <- ggplot(d, aes(i, value, linetype=variable)) +
    geom_hline(yintercept=700^2) +
    geom_line() +
    scale_linetype_manual(values=c(2,1)) +
    scale_x_continuous(breaks=(0:20)*365/7, labels=0:20) +
    scale_y_sqrt() +
    annotate('text', 8*365/7, 1e3,
             label="P(italic(i))==8~italic(i)", parse=TRUE,
             hjust=1, size=3) +
    annotate('text', 8*365/7, 2.5e5,
             label="A(italic(i))==1+4~italic(i)(italic(i)-1)", parse=TRUE, 
             hjust=1, size=3)

enter image description here

score 7 · Answer 3 · edited May 23 '17 at 12:02

Best rated answer is just fine, but in a more complex scenario with linebreaks it did not work for me, so I simply used Unicode italic characters instead. For your example:

library(Unicode)

italic_i <- u_char_inspect(u_char_from_name("MATHEMATICAL ITALIC SMALL I"))["Char"]
label1 <- paste("P(", italic_i, ")=8", italic_i, sep="")
label2 <- paste("A(", italic_i, ")=1+4", italic_i, "(", italic_i, "-1)", sep="")

i <- 1:(8*365/7)
d <- data.frame(i=i,p=p(i),a=sapply(i,a))
d <- melt(d, id.vars='i')
p <- ggplot(d, aes(i, value, linetype=variable)) +
  geom_hline(yintercept=700^2) +
  geom_line() +
  scale_linetype_manual(values=c(2,1)) +
  #geom_point() +
  scale_x_continuous(breaks=(0:20)*365/7, labels=0:20) +
  #scale_y_continuous(breaks=c(0,700^2), labels=c(0,expression(L^2)))
  scale_y_sqrt() +
  #scale_y_log10() +
  annotate('text', 8*365/7, 1e3, label=label1, hjust=1, size=3) +
  annotate('text', 8*365/7, 2.5e5, label=label2, hjust=1, size=3)
print(p + theme_classic())

Edit: I have just noticed that saving a pdf with pdf() doest not render unicode correctly, but you can simply use cairo_pdf() instead, which works just fine (see: Unicode Characters in ggplot2 PDF Output)

score 2 · Answer 4 · answered Dec 18 '20 at 00:19

For simple text formatting, use the ggtext package

If you do not regularly use plotmath, and find it easier to use simple markdown/html style text formatting- use the recently added ggtext package

Adding the reference to the newer ggtext package here- even though this example is simpler than the OP question (along the lines of @pbnelson)

library(ggplot2)
library(ggtext)
#> Warning: package 'ggtext' was built under R version 4.0.3
library(tibble)
#> Warning: package 'tibble' was built under R version 4.0.3
dfx <- tibble(x=seq(0,3.14,0.01))
ggplot(dfx, aes(x, sin(x))) +
  geom_line() + # works the same for qplot or ggplot
    geom_richtext(x = 1.5, 
                  y = 0.5, 
                  label.color = NA,
                  label = "<i><b>Hello</i></b>, World<br>You can even do 
                  Some <span style='color:blue'>blue text **in bold.**</span><br>And *italics text.*"
                  )

^{Created on 2020-12-17 by the reprex package (v0.3.0)}

ggplot format italic annotation

4 Answers4