knitr changes (1) to <ol> when rendering html?

Question

The following content of a .Rmd file:

---
title: "Untitled"
output:
  html_document: default
---

```{r cars}
mtcars$am <- sprintf("(%s)", as.character(mtcars$am))
knitr::kable(mtcars, format = "html")
```

Will show ordered lists <ol><li></li></ol> in the am column, instead of the numbers in brackets (as produced with the sprintf) after rendering to html.

Is this intended? How can I work around this and have numbers in brackets show as they are in the html output?

The output of knitr::kable seems to be fine, showing:

<td style="text-align:left;"> (1) </td>

Details:

• Using knitr 1.20
• RStudio Server 1.1.453
• note that removing format = "html" does not resolve the issue as in the real-life context I would like to do advanced formatting with css e.g. based on the classes of the produced tables

A quick workaround solution based on Michael Harper's accepted answer may be a method like so:

replacechars <- function(x) UseMethod("replacechars")
replacechars.default <- function(x) x
replacechars.character <- function(x) {
  x <- gsub("(", "&lpar;", x, fixed = TRUE)
  x <- gsub(")", "&rpar;", x, fixed = TRUE)
  x
}
replacechars.factor <- function(x) {
  levels(x) <- replacechars(levels(x))
  x
}
replacechars.data.frame <- function(x) {
  dfnames <- names(x)
  x <- data.frame(lapply(x, replacechars), stringsAsFactors = FALSE)
  names(x) <- dfnames
  x
}

Example use:

mtcars <- datasets::mtcars

# Create a character with issues
mtcars$am <- sprintf("(%s)", as.character(mtcars$am))

# Create a factor with issues
mtcars$hp <- as.factor(mtcars$hp)
levels(mtcars$hp) <- sprintf("(%s)", levels(mtcars$hp))

replacechars(mtcars)

Answer 1

If you don't want to remove the format="html" argument, you could try using the HTML character entities for the parentheses (&lpar and &rpar) and then add the argument escape = FALSE:

```{r cars}
mtcars$am <- sprintf("&lpar;%s&rpar;", as.character(mtcars$am))
knitr::kable(mtcars, format = "html", escape = FALSE)
```

Still not entirely sure of what is causing the error though. It seems that the specific combination of parentheses is being processed strangely by knitr.

Answer 2

An alternative solution is to escape the parentheses, e.g.,

mtcars$am <- sprintf("\\(%s)", as.character(mtcars$am))

Then you won't need escape = FALSE.

See https://pandoc.org/MANUAL.html#backslash-escapes in Pandoc's Manual.