LaTeX math in base R graphics

A first plot

library(gridmicrotex)
library(grid)

latex_options(device_math = TRUE)

plot(1:10, (1:10)^2,
     main = r"(Slope $\hat{\beta}_1 = \sum_{i=1}^{n} x_i^2$)",
     xlab = "Cost $5-$10 per unit",
     ylab = r"($\frac{y}{2}$)")
text(3, 80, r"($\int_0^\infty e^{-x^2}\,dx$)", col = "steelblue")

The title, y-axis label and annotation are typeset. The x-axis label has no math in it, so it is drawn as written.

In R Markdown, set the option in the setup chunk. If you turn it off, do so in a later chunk than the plot, or the plot shows the literal $...$.

More than plotmath

Tables, display-style operators and other LaTeX work in any label. The coefficient table below is drawn by an ordinary text() call:

set.seed(42)
x   <- seq(0, 3, length.out = 60)
y   <- 2 + 1.4 * x^2 + rnorm(60, sd = 1.1)
fit <- lm(y ~ poly(x, 2, raw = TRUE))
cf  <- signif(coef(summary(fit)), 3)

title_eq <- r"($$\hat{y} = \beta_0 + \beta_1 x + \beta_2 x^2$$)"

# Make room for the tall title
h   <- latex_dims(title_eq, gp = gpar(fontsize = par("ps")))$height
top <- ceiling(convertHeight(h, "bigpts", TRUE) /
               (par("cin")[2] * 72 * par("mex"))) + 2

par(mar = c(4.5, 5.5, top, 2))
plot(x, y, pch = 19, col = "grey45", cex = 0.7, ylim = c(0, 22),
     main = title_eq, xlab = r"($x$)",
     ylab = r"($y = f(x) + \varepsilon$)")
lines(x, predict(fit), col = "#B22222", lwd = 2)

# Build the table as a single line of text
tab <- sprintf(paste0(
  r"(\begin{array}{|l|r|r|}\hline)",
  r"(\rowcolor{#E8F0FE}\text{Term} & \hat{\beta} & \text{SE}\\\hline)",
  r"(\beta_0 & %s & %s\\)",
  r"(\beta_1 & %s & %s\\)",
  r"(\beta_2 & %s & %s\\\hline\end{array})"),
  cf[1, 1], cf[1, 2], cf[2, 1], cf[2, 2], cf[3, 1], cf[3, 2])

text(0.05, 18, tab, adj = c(0, 0.5), cex = 0.75)
text(2.95, 1.2, r"($\varepsilon \sim \mathcal{N}(0, \sigma^2)$)",
     adj = c(1, 0), cex = 0.95, col = "#B22222")

Two tips from this example:

• Keep a formula on one line. A label containing a newline is not recognised as math.
• Anchor a tall label by its centre (adj = c(0, 0.5)) and leave room around it; see Tall formulas.

Other packages

The option works for any plot drawn on an R graphics device: base plot methods such as plot(lm), hist() and legend(), lattice, grid, and ggplot2 (axis titles, geom_text(), facet strips, legend keys). It does not reach plotly or rgl’s text3d() labels.

For ggplot2, geom_latex() and element_latex() are often the better choice; see vignette("ggplot2-integration").

When is a label treated as math?

A label is typeset only when every $ in it is closed and each $...$ pair holds something that looks like math. Everyday dollar signs are left alone:

$$...$$, \(...\) and \[...\] also work. Write \$ for a literal dollar sign in a label that also has math.

Tall formulas

Widths are measured correctly, but heights are not: R sizes margins, titles and legend() boxes for one line of text, so a tall formula can overflow them. Measure it with latex_dims() and widen the margin:

h  <- latex_dims(r"($\frac{a}{b}$)", gp = gpar(fontsize = par("ps")))$height
bp <- convertHeight(h, "bigpts", TRUE)

# Lines of margin needed
bp / (par("cin")[2] * 72 * par("mex"))
#> [1] 1.041667

Round that up and add it to the matching side of par(mar = ).

Limitations

• The option applies to every plot in the session, including plots from other packages. Labels without math are not changed.
• Math is drawn as outlines, so it cannot be selected in a PDF or SVG.
• Bold comes from \textbf{}, not from the plot’s font face.
• \includegraphics is skipped, and rounded box corners are square.
• A label that cannot be read is drawn as plain text, without a warning.
• It does not work together with showtext::showtext_auto().
• expression() labels are not affected.
• corrplot reads a label starting with $ itself; start it with something else.