Make R Markdown code blocks into math mode

Question

I would love to use R Markdown to generate homework and exam solutions, but I would prefer to have them more readable to non-coders.

I there a way that I can pass the ECHO output through math mode? That is I would love to have an ECHO that looks more "inline" and less like code. I can see how to hide it, but in the R Markdown Reference Guide I don't see an option to remove the "code block" and wrap each line in $$ (or wrap in anything). Is there a way to do this?

Here is an example. This solution has all the meat, but may be a little intimdating to some students (this is not an R course).

8-22 ...

a. ...

```{r part_a}

D_0 = 2.40
g = 0.06
r = 0.12

V = D_0*(1 + g)/(r - g)
V
```

Instead, I would love to see something more like the following.^[I appreciate that I can generate this output with some cutting and pasting and a text editor, I am just trying to find the most efficient solution, since this is likely something that I will do more than once or twice.]

8.22 ...

a. ...

$$ D_0 = 2.40 $$
$$ g = 0.06 $$
$$ r = 0.12 $$
$$ V = D_0 \times (1 + g)/(r - g) = 2.40 \times (1 + 0.06)/(0.12 - 0.06) = `r V`$$

Answer 1

I have a partial answer. I don't yet know how to replace variable x with its value so that a can print the formula with variables, replaced by numbers. But I can generate the "math code" block so that I can solve the problem and generate the pretty solution without a lot of cut and paste.

Here is an example .Rmd file.

---
author: Richard Herron
title: Homework Solutions
---

8-22 ...

a. ...

There are three parts to this solution.

1. write the equations to solve the problem in R-readable strings.
2. loop over the list and `eval(parse())` the equation strings
3. wrap strings in `$$ $$` with `cat(paste0())`

Chunks should be set to `echo=FALSE` and `results="asis`. You may need to suppress some function output with `invisible()`.


```{r part_a, echo=FALSE, results="asis"}

# just to make sure my eval below works 
rm(list=ls())

# store solution as a list of character equations
solution <- list(
"D_0 = 2.40", 
"g = 0.06", 
"r = 0.12", 
"V = D_0*(1 + g)/(r - g)"
)

# "solve" problem
for (i in seq_along(solution)) eval(parse(text=solution[[i]]))

# display solution as math
cat(paste0("$$", solution, "$$"), sep="\n")
```

Because of the `eval()` loop in the first chunk I can say that $V = `r V`$ in the text that follows.

And here is an outer file that convert each .Rmd file into a .pdf.

# load `render` and set working directory
setwd("C:/Users/Richard/Dropbox/Babson College/SME 2021 for 2015 fall/Homework")

# loop over all Rmd files
require(rmarkdown)
require(tools)
files <- list.files(path=".", pattern="*.Rmd")
roots <- sapply(files, file_path_sans_ext)
namesIn <- paste0("", roots, ".pdf")
namesOut <- paste0("", roots, ".pdf")

# solutions
myPdf <- pdf_document(
    fig_caption=TRUE,
    keep_tex=TRUE,
    pandoc_args=c(
        "--variable=classoption:fleqn", 
        "--variable=classoption:twocolumn", 
        paste0("--metadata=date:", format(Sys.time(), "%B %d, %Y"))
        )
    )
lapply(files, FUN=render, output_format=myPdf)
mapply(file.rename, namesIn, namesOut)

Which yields this pdf.