Rmarkdown, plot title font as latin modern

Question

I have an knitr document with single plot. I want to use the original fonts of R in the plot except the axis labels which should come from latin modern. I can use latin modern for all the fonts in the plot by tikzDevice package of R. But compiling this takes too much time when the data set used for plotting is very big.

OR, Can I use tikzDevice only for labels and title of the plot?

A summary code is below:

<<setup, include=FALSE, cache=FALSE>>=
library(knitr)
library(tikzDevice)
#opts_chunk$set(dev = 'tikz') # I don't want to use tikzDevice.
opts_chunk$set(dev.args=list(pointsize=12)) 
@

<<tikzfigure, echo = FALSE, fig.width = 4, fig.height = 4, fig.align = 'center', fig.pos = 'ht', tidy = TRUE>>=

plot(1:5,1:5,xlab=paste0("$\\sum \\beta_i$"))
@

The output:

The plot should stay as the same except the x label should be

(latin modern font.)

How can I achieve this?

(Note: I asked the question stackoverflow as well, but I think this is the correct place for it. I don't know if this is a problem...)

Answer 1

You can use the latex2exp library to parse the LaTeX code in your label. Make sure you have a font that contains the italic beta. I used I used CM-Unicode. You can access the glyph using the unicode representation \u03B2 or as the character β.

Here is a complete MWE in knitr (.Rnw file):

\documentclass[border=3pt]{standalone}

<<setup, include=FALSE, cache=FALSE>>=
rm(list = ls())
library(knitr)
library(latex2exp)
library(showtext)
font_add("CMUSerif-RomanSlanted",regular="c:/windows/fonts/cmunsl_0.ttf")
#library(tikzDevice)
#opts_chunk$set(dev = 'tikz') # I don't want to use tikzDevice.
opts_chunk$set(dev.args=list(pointsize=12))
@

\begin{document}
<<chunk1, echo = FALSE, fig.width = 4, fig.height = 4>>=
plot(1:5,1:5,xlab=TeX("$\\sum \\textit{\u03B2_i}$"))
plot(1:5,1:5,xlab=TeX("$\\sum \\textit{\u03B2_i}$",list(family="CMUSerif-RomanSlanted")))
plot(1:5,1:5,xlab=TeX("$\\sum \\textit{β_i}$",list(family="CMUSerif-RomanSlanted")))
@
\end{document}

Giving this: