Mathematical Annotation in R

• R Core Team (R-core@R-project.org ) The R Project for Statistical Computing.
• Lijia Yu (yu@lijiayu.net / GitHub / Twitter) A master candidate majoring in Bioinformatics at Beijing Institute of Genomics.
• Karl Broman (kbroman@biostat.wisc.edu / GitHub / Twitter) Department of Biostatistics and Medical Informatics, University of Wisconsin-Madison; research in statistical genetics; developer of R/qtl (for R)
• Kevin Ushey (kevinushey@gmail.com / GitHub / Twitter) MSc., University of British Columbia; interested in statistical genetics and data visualization

Want to write mathematical symbols and expressions in R graphics? You can use an R expression() instead of normal text, e.g. plot(1:10, main = expression(alpha + beta)). Below is a demo that shows you everything about plotting math in R (it was written by the R Core Team; see ?plotmath for details):

demo(plotmath)

Combining expressions and text

If you want to combine multiple mathematical expressions with text, use paste() inside expression(), as in the following.

par(mar = c(4, 4, 2, 0.1))
plot(rnorm(100), rnorm(100),
  xlab = expression(hat(mu)[0]), ylab = expression(alpha^beta),
  main = expression(paste("Plot of ", alpha^beta, " versus ", hat(mu)[0])))

Finally, if we want to include variables from an R session in mathematical expressions, and substitute in their actual values, we can use substitute().

par(mar = c(4, 4, 2, 0.1))
x_mean <- 1.5
x_sd <- 1.2
hist(rnorm(100, x_mean, x_sd),
  main = substitute(
    paste(X[i], " ~ N(", mu, "=", m, ", ", sigma^2, "=", s2, ")"),
    list(m = x_mean, s2 = x_sd^2)
  )
)