How to write reproducible comment in rmarkdown

Can anyone help in how to write a reproducible comment in Rmarkdown?

For example, we have the data set as shown below:

In Rmarkdown report comments are typed using # before the text within code chunk. I want to write a reproducible comment for mean age.

# The average age is 45

Is there any way to write the above comment as reproducible? In case I change the values for age variable, the average value should automatically updated in the comment...

I would be thankful for your kind support.

Regards, Farhan

Option 1

One option could be generating the code chunk dynamically using chunk option results="asis".

---
title: "Reproducible comments"
output: html_document
---

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

## R Markdown

```{r dt, echo=FALSE}
df <- tibble::tribble(
  ~age, ~fnlwgt, ~education_num,
   39L,  77516L,            13L,
   50L,  83311L,            13L,
   38L, 215646L,             9L,
   53L, 234721L,             7L
  )

```


```{r results="asis", echo=FALSE}
cmnt <- paste0(
"```{r}\n",
"df <- tibble::tribble(
  ~age, ~fnlwgt, ~education_num,
   39L,  77516L,            13L,
   50L,  83311L,            13L,
   38L, 215646L,             9L,
   53L, 234721L,             7L
  )\n\n",
"# The average age is ", mean(df$age), "\n",
"```\n"
)

cat(cmnt)
```

---

---

Option 2

Another option could be using knitr::knit_expand to dynamically expand the comments with {{}} in a template r-markdown file.

Suppose this is the template r-markdown file,

---

template.Rmd

```{r}
mean_age <- mean(dat$age)
# The mean age is {{age}}

mean_educ <- mean(dat$education_num)
# The mean education_num is {{educ}}
```

---

Now to expand these comments in our main document, we use knitr::knit_expand and pass the variable to be expanded in the comments, and then we add the contents of template.Rmd using knitr::knit_child.

---
title: "Reproducible comments"
output: 
  html_document:
    keep_md: TRUE
---

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

## R Markdown

```{r}
dat <- tibble::tribble(
  ~age, ~fnlwgt, ~education_num,
   39L,  77516L,            13L,
   50L,  83311L,            13L,
   38L, 215646L,             9L,
   53L, 234721L,             7L
  )
```

## Comments reproduced dynamically

```{r, echo=FALSE, results='asis'}
src = knitr::knit_expand(
  "template.Rmd", 
  age = mean(dat$age), 
  educ = mean(dat$education_num)
)

res = knitr::knit_child(text = src, quiet = TRUE)
cat(res, sep = '\n')
```

---

---