How can I make inline r script visible in RMarkdown report?

Question

Suppose that the command isn't important enough to have it on the separate line, But I still want it to be visible along the result, I know there is ` r inlinestr` in R Markdown, but it I can't pass echo=T to it. I want the result to be something like this:

Answer 1

I just ran across this question that I attempted to answer about two years ago and thought of a way to get both the code and its evaluated output in a single inline statement. We just need a helper function. Below is an example. The code is entered as a text string and the function returns both the code and the result of evaluating the code:

---
title: "RMarkdown teaching demo"
author: "whoever"
output: pdf_document
---

```{r}
fnc = function(expr) {
  paste(expr, " = ", eval(parse(text=expr)))
}

# Add some missing values
iris$Sepal.Length[c(3,5,10)] = NA
```

f. There are `r fnc("sum(is.na(iris$Sepal.Length))")` missing height values.

Below is the output.

---

---

It works, but there are two issues. First, the code is not in monospace font. Second, the code is not highlighted with a gray background.

I thought that I could get monospace font with the latex \texttt{} tag.

```{r}
fnc = function(expr) {
  paste("\\texttt{", expr, " = ", eval(parse(text=expr)), "}", sep="")
}
```

This appears to return the desired string when run interactively ("\\texttt{sum(is.na(iris$Sepal.Length)) = 3}"), but throws the following error when I try to knit the document:

! Extra }, or forgotten $.
<recently read> \egroup

l.163 ...texttt{sum(is.na(iris$Sepal.Length)) = 3}

I thought I could get highlighting with the \hl{} tag (which also requires \usepackage{color, soul} in the latex header):

```{r}
fnc = function(expr) {
  paste("\\hl{", expr, " = ", eval(parse(text=expr)), "}", sep="")
}
```

However, once again, this throws an error:

! Argument of \SOUL@addmath has an extra }.
<inserted text> 
                \par 
l.161 ...re \hl{sum(is.na(iris$Sepal.Length)) = 3}

Both texttt{} and \hl{} work without a problem when used with regular text inside an rmarkdown document.

So, I'm not sure how to get the monospace font or highlighted text, but at least this takes a step toward code + evaluated code from a single inline R statement. Hopefully, someone with more knowledge of computing on the language and outputting latex markup can provide more insight into how to get this to work as desired.