latex2exp

latex2exp is an R package that parses and converts LaTeX mathformulas to R’s plotmathexpressions.Plotmath expressions are used to enter mathematical formulas and symbolsto be rendered as text, axis labels, etc. throughout R’s plottingsystem. I find plotmath expressions to be quite opaque, while LaTeX is ade-facto standard for mathematical expressions, so this package might beuseful to others as well.

Installation

Install this package from CRAN:

install.packages('latex2exp')

You can also install from GitHub usingdevtools:

devtools::install_github('stefano-meschiari/latex2exp')

Usage

library(latex2exp)

The TeX function takes a LaTeX string and returns a plotmathexpression suitable for use in plotting, e.g.,

TeX('$\\gamma^\\alpha$')

Before R 4.0, it is necessary to escape the backslash within the stringliteral: therefore, one writes '$\\gamma$' rather than '$\gamma$'(the latter will cause an error).

After R 4.0, it is recommended to use the new raw string literal syntax(see ?Quotes). The syntax looks like r"(...)", where ... cancontain any character sequence, including \:

TeX(r'($\gamma^\alpha$)')

The return value of TeX() can be used anywhere a plotmath expressionis accepted, including plot labels, legends, and text.

The following example shows plotting in base graphics:

x <- seq(0, 4, length.out=100)
alpha <- 1:5

plot(x, xlim=c(0, 4), ylim=c(0, 10), 
     xlab='x', ylab=TeX(r'($\alpha  x^\alpha$, where $\alpha \in 1 \ldots 5$)'), 
     type='n', main=TeX(r'(Using $\LaTeX$ for plotting in base graphics!)', bold=TRUE, italic=TRUE))

invisible(sapply(alpha, function(a) lines(x, a*x^a, col=a)))

legend('topleft', legend=TeX(sprintf(r'($\alpha = %d$)', alpha)), 
       lwd=1, col=alpha)

This example shows plotting in ggplot2:

library(purrr)
library(ggplot2)
library(tibble)

x <- seq(0, 4, length.out=100)
alpha <- 1:5
data <- map_df(alpha, ~ tibble(v=.*x^., x=x, alpha=.))

p <- ggplot(data, aes(x=x, y=v, color=as.factor(alpha))) +
    geom_line() + 
    ylab(TeX(r'($\alpha  x^\alpha$, where $\alpha \in 1\ldots 5$)')) +
    ggtitle(TeX(r'(Using $\LaTeX$ for plotting in ggplot2. I $\heartsuit$ ggplot!)')) +
    coord_cartesian(ylim=c(-1, 10)) +
    guides(color=guide_legend(title=NULL)) +
    scale_color_discrete(labels=lapply(sprintf(r'($\alpha = %d$)', alpha), TeX)) 
    # Note that ggplot2 legend labels must be lists of expressions, not vectors of expressions

print(p)

You can quickly test out what a translated LaTeX string would look likeby using plot:

plot(TeX(r'(A $\LaTeX$ formula: $\frac{2hc^2}{\lambda^5} \, 
               \frac{1}{e^{\frac{hc}{\lambda k_B T}} - 1}$)'), cex=2)

Syntax

Use

TeX(r'(My string containing math $\sin(2\pi\lambda x)$)')

to build a plotmath expression, ready for use in plots. If the parsercannot build a correct plotmath expression, it will stop() and showthe invalid plotmath expression built.

Add parameters bold=TRUE or italic=TRUE to make the entire labelbold or italic:

TeX(r'(My string containing math $\sin(2\pi\lambda x)$)', bold=TRUE, italic=TRUE)

TeX('latexString', output=c('expression', 'character', 'ast'))

If the output option is equal to character, it will return thestring representation of the expression (which could be converted intoan expression using parse(text=)).

If the output option is equal to ast, it will return the tree builtby the parser (this is only useful for debugging).

latex2exp_examples()

will show a demo of the supported LaTeX syntax.

latex2exp_supported(plot=FALSE)

returns a list of supported LaTeX. If plot=TRUE, a table of symbolswill be plotted.

Supported LaTeX

Formulas should go between dollar characters ($).

Only a subset of LaTeX is supported. Greek symbols (\alpha, \beta,etc.) and the usual operators (+, -, etc.) are supported. Theirrendering depends on R’s interpretation of the plotmath expression.

In addition, the following should be supported:

latex2exp_supported(plot=TRUE)

A few examples:

latex2exp_examples()

## [1] TRUE

Changes

0.5.0 [03/14/2020]

• Adds parameters bold and italic to TeX(). These can be used tomake the entire expression bold or italic.
• Adds \phantom{}(PR)

0.4.0 [08/29/2015]

• Deprecated the latex2exp() function; use TeX() instead.
• Added \lbrack and \rbrack to type left and right squarebrackets.

0.3.3 [08/11/2015]

Fixes bug #4 (“fix parsing of numbers”), where certain numbers insideformulas where not parsed correctly.

0.3.2 [07/28/2015]

Fixes bug #3 (“subscript and superscript style”). latex2exp nowrenders combined subscripts and superscripts correctly.

0.3.1 [07/02/2015]

Fixes bug #2 (white space causes unexpected behaviour). latex2expshould now be a bit more compliant with how LaTeX handles whitespace.

0.3.0 [06/30/2015]

latex2exp is now a proper package.

0.2.0 [06/29/2015]

Formulas must now be enclosed between dollar characters ($), as in LaTeXproper. Text does not need to be enclosed in \text tags anymore.