README.md

In tomicapretto/latex2r: Translate Latex Formulas to R Code

latex2r

The goal of latex2r is to translate LaTeX formulas to R code.

Installation

You can install the development version from GitHub with:

# install.packages("devtools")
devtools::install_github("tomicapretto/latex2r")

This is a very young package so it may not work as expected if you try to translate things outside of the supported syntax. Please refer to Supported LaTeX section for more information about it.

Examples

Just some basic funcionality: translate LaTeX to R.

library(latex2r)
latex2r("\\beta_1^{\\frac{x+1}{x^2 \\cdot y}}")
#> [1] "beta_1^((x + 1) / (x^2 * y))"

With a combination of parse() and eval() you can evaluate the translated expression. Of course, names must be bound to a value if we expect this to work.

eval(parse(text = latex2r("\\pi * \\sin(\\frac{x}{2})")), envir = list(x = pi))
#> [1] 3.141593

There is an extra feature which is possible due to R is so permissive. latex2fun() receives a LaTeX expression that represents the definition of a mathematical function and returns an R function that computes the function value and has arguments representing all the variables involved in the function.

x = seq(-2*pi, 2*pi, length.out = 500)
f = latex2fun("\\sin{a * x}^2 + \\cos{b * x} ^2")
print(f)
#> function (a, b, x) 
#> sin(a * x)^2 + cos(b * x)^2

y = f(x = x, a = 2, b = 3)
plot(x, y, type = "l")

This is experimental but I think it is so cool that it is worth a chance in the package. For those who like to play with R most weird features, they would find the source code is a nice place.

In addition, if you call latex2r(interactive=TRUE) it launches a REPL that you can use interactively.

Supported LaTeX

Only a small subset of LaTeX expressions are suported so far. However, these are enough to define a very wide set of mathematical functions.

Greek letters supported

The following greek letters are supported as identifiers (variable names).

latex2r:::get_pkg_data('GREEK_KEYWORDS')
#>  [1] "\\alpha"      "\\theta"      "\\tau"        "\\beta"       "\\vartheta"  
#>  [6] "\\pi"         "\\upsilon"    "\\gamma"      "\\varpi"      "\\phi"       
#> [11] "\\delta"      "\\kappa"      "\\rho"        "\\varphi"     "\\epsilon"   
#> [16] "\\lambda"     "\\varrho"     "\\chi"        "\\varepsilon" "\\mu"        
#> [21] "\\sigma"      "\\psi"        "\\zeta"       "\\nu"         "\\varsigma"  
#> [26] "\\omega"      "\\eta"        "\\xi"         "\\Gamma"      "\\Lambda"    
#> [31] "\\Sigma"      "\\Psi"        "\\Delta"      "\\Xi"         "\\Upsilon"   
#> [36] "\\Omega"      "\\Theta"      "\\Pi"         "\\Phi"

Syntax supported

You can use the following operators

• Unary:
  • + and -.
• Binary:
  • +, -, *, /, ^, and _.
• Grouping:
  • {...}, \left{...\right}, (...), and \left(...\right).

And the following functions

• Unary:
  • \sqrt, \log, \sin, \cos, \tan, \cosh, \sinh, and \tanh.
• Binary:
  • \frac{...}{...}, \cdot, and \times.

Notes

• The operator _ is used to represent subscripts. While you can do (5_2) in LaTeX, it is not allowed in the package since a subscript on a number does not make sense. Only variable names (such as x or \\pi) can have subscripts.
• In latex you can write \sqrt[p]{x} to represent the p-th root. However this is not allowed in this package (at least for now). To represent a p-th root you can use x^{1/p}.

Some remarks

Implicit multiplication

tl;dr: xy is understood as x times y.

A previous version of this package required multiplication to be explicit. For example, xy would have been understood as an identifier called xy. Now, all identifiers, except from special ones (greek letters), are of one character only. If you do abc^5 it will be understood as a*b*c^5.

In addition, you can still pass an explicit multiplication operator such as *, \times or \cdot.

Explicit grouping

Although something like \sin5 renders as (\sin5) and we all understand this means sine of 5, we require explicit grouping with {} or () to avoid ambiguity in the function argument. What if I write \sin5a? Does it mean a times the sine of 5 or the sine of 5 times a? Explicit grouping is a simple solution to eliminate this ambiguity.

Special treatment for some characters

Since the numbers and are so common in mathematical expressions they are treated as constant numbers and not as names of variables.

In R is a built-in constant number and is obtained with exp(1). See the next example

latex2r("\\sin{2 * \\pi * t}")
#> [1] "sin(2 * pi * t)"
latex2r("e * x")
#> [1] "exp(1) * x"
latex2r("e^{x + i * y}")
#> [1] "exp(x + i * y)"

But note that complex numbers are not supported (yet?).

Logarithm of different base

If you write \\log(x) it will be interpreted as the natural logarithm of x. If you write \\log_n(x) it will be interpreted as the logarithm of x with base n.

latex2r("\\log(x + 1)")
#> [1] "log(x + 1)"
latex2r("\\log_2(x + 1)")
#> [1] "log(x + 1, base = 2)"

Examples

| LaTeX | R Code | | :------------------------------------------------------------- | :--------------------------------------------------------------- | | x + y | x + y | | \sin(x) + \cos(y) | sin(x) + cos(y) | | \sin(x)^2 + \cos(y)^2 | sin(x)^2 + cos(y)^2 | | \sqrt{2x\pi} | sqrt(2 * x * pi) | | \log(z) | log(z) | | \log_a(\frac{x^5}{y}) | log((x^5) / y, base = a) | | \frac{1}{\sigma\sqrt{2\pi}}e^{\frac{(x - \mu)^2}{2\sigma^2}} | 1 / (sigma * sqrt(2 * pi)) * exp(((x - mu)^2) / (2 * sigma^2)) | | \beta_1^{\frac{x+1}{x^2 \cdot y}} | beta_1^((x + 1) / (x^2 * y)) |

tomicapretto/latex2r documentation built on Sept. 20, 2021, 3:07 p.m.