可以使用unicode表示(u00B1):

It is possible to use the unicode representation (u00B1):

a <- ggplot()
a <- a + geom_point(aes(x=seq(0,1,0.1), y=seq(0,1,0.1)))
a <- a + annotate("text", x=0.5, y=0.3, label="myplot")
a + annotate("text", x=0.5, y=0.2, label="u00B1")

或者您可以直接使用 ± 符号，方法是从某处复制和粘贴它.

Or you can use the ± symbol directly, by copying and pasting it from somewhere.

a + annotate("text", x=0.5, y=0.2, label="±")