Understanding Unicode Characters and Knitting to PDF with R Markdown

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As a technical blogger, I’m often asked about various issues related to knitting R Markdown documents to PDF. Recently, I received a question from a user who was experiencing difficulties displaying unicode characters in their knitted PDFs. In this article, we’ll delve into the world of unicode characters, explore how they’re represented in R source code, and discuss strategies for effectively including them in your R Markdown documents when knitting to PDF.

Understanding Unicode Characters

Before we dive into the specifics of R Markdown and knitting to PDF, it’s essential to understand what unicode characters are. Unicode is a character encoding standard that provides a unique number for each character, symbol, or emoji used across different languages and devices. This allows us to represent a wide range of symbols, including those found in various languages.

In R source code, unicode characters can be represented using different escape sequences. The most common approach involves using the \U escape sequence, which is used for Unicode code points greater than 0xFFFF.

For example, if you want to display the chinese character “street” (, 街) in your R Markdown document, you would use the following code:

cat("This is chinese: \U8857\n")

Knitting to PDF with R Markdown

When knitting an R Markdown document to PDF, R uses LaTeX as its primary output format. The way unicode characters are rendered in the final PDF depends on the LaTeX engine used.

In the provided example, the user had set the latex_engine option to xelatex, which is a more modern and powerful version of LaTeX that supports advanced features like Unicode rendering. However, even with this configuration, the user was still unable to display certain unicode characters in their knitted PDFs.

Solutions

After examining the code provided by the user, it became apparent that there were two main issues:

The user had used the incorrect escape sequence for the unicode character “\U8857”. Instead of \U8857, they should have used "\U8857" to correctly represent the escape sequence.
Even with the correct escape sequence, the user needed a font that supported the required glyphs. In this case, they had set the mainfont option in their R Markdown document configuration to Noto Sans CJK SC, which is a font that includes glyphs for various asian languages.

To resolve these issues, I recommended that the user update their code as follows:

---
output:
  pdf_document:
    latex_engine: xelatex
mainfont: Noto Sans CJK SC
---



```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = TRUE,warning=FALSE)

library("readxl")
library("knitr")
library("kableExtra")
library("dplyr")
library("reshape2")


df1 &lt;- data.frame(ID = c("A", "B", "C", "D", "E"),
                  spider = c(0.05, 0.01, 0.1, 0.01,0.01),
                  beetle = c(0.09, 0.01, 0.05, 0.05, 0.1))

df1 &lt;- df1 %>% 
  mutate(
    spider = ifelse(spider == 0.05, "\U8857", 
                   ifelse(spider == 0.09, "\U8413", 
                           ifelse(spider == 0.01, "\U9210", 
                                   "\U821"))),
    beetle = ifelse(beetle == 0.09, "\U8413", 
                   ifelse(beetle == 0.05, "\U8414", 
                           ifelse(beetle == 0.05, "\U8414", 
                                   "\U822"))))


df1 %>% kable("markdown", align="c", bookmarks=T)

The updated code uses the correct escape sequence for the unicode character and includes a font that supports the required glyphs.

Conclusion

In conclusion, displaying unicode characters in R Markdown documents can be challenging when knitting to PDF. However, by understanding how unicode characters are represented in R source code and using the correct configuration options, it is possible to effectively include these characters in your knitted PDFs.

We’ve discussed the use of the \U escape sequence for unicode characters, explored different font options that support glyphs for various languages, and provided an updated example of how to knit an R Markdown document with unicode characters. By following these guidelines, you should be able to successfully display a wide range of symbols in your knitted PDFs.

I hope this article has helped you better understand the intricacies of knitting R Markdown documents to PDF and how to effectively include unicode characters in your output.

Last modified on 2024-06-08