Use loop to generate section of text in rmarkdown

Question

I need to produce a report that is composed of several sections, all sections look similar, with only some differences in data. The number of sections is also dependent on the data. What I ultimately want to have is something like this:

```{r}
  section_names = c("A","B","C")
  section_data = c(13,14,16)
```

# some looping mechanism here with variable i

This is section `r section_names[i]`

This section's data is `r section_data[i]`

#more things go here for the section

#end of loop should go here

The result should be a single html/document with all the sections one after the other.

Can you point me to a way for producing such an Rmd file with the loop?

Ideally I would have hoped to see something like in PHP:

<$php for(i=0;i<10;i++) { ?>
   ## some html template + code chunks here
<$php } ?>

Answer 1

This question is similar to that one, although it is LateX/RNW based. Besides, this answer demonstrates how to generate a rmarkdown document dynamically. However, neither of the questions is a exact duplicate of this one.

Basically, there are two mental steps to take:

• Figure out the markdown markup needed per section. This could be something along the lines of

  ## This is section <section_name>
  Section data is `<section_data>`.
  Additional section text is: <section_text>.
  

• Write R code that generates this markup, replacing the placeholders with the appropriate values.

For step 2, using sprintf is a natural candidate to combine static and dynamic text. Don't forget to use the chunk options results = "asis" to prevent knitr from adding formatting to your output and use cat (instead of print) to prevent R from adding additional stuff like quotes and element numbers.

I changed the input data structure a little bit for the sake of clarity (using a data.frame instead of independent vectors section_names and section_data).

```{r echo = FALSE, results = "asis"}
input <- data.frame(
  name = LETTERS[1:4],
  data = runif(n = 4),
  text = replicate(4, paste(sample(x = LETTERS, size = 100, replace = TRUE), collapse = "")),
  stringsAsFactors = FALSE)

template <- "## This is section %s
Section data is `%0.2f`.
Additional section text is: %s.

" # dont't forget the newline

for (i in seq(nrow(input))) {
  current <- input[i, ]
  cat(sprintf(template, current$name, current$data, current$text))
}
```

Output:

This is section A

Section data is 0.83. Additional section text is: PUFTZQFCYJFNENMAAUDPTWIKLBSVKWMJWODFHSPRJRROTVDGNEROBVQPLLMVNPOUUHGVGRPMKAOAOMVYXKMGMUHNYWZGPRAWPYLU.

This is section B

Section data is 0.49. Additional section text is: PFTYCGFSGSMAYSSCZXWLNLDOQEBJYEVSJIYDJPEPSWQBNWJVRUKBTYIUSTOICFKJFEJCWCAYBCQSRTXUDEQLLXCZNPUKNLJIQJXE.

This is section C

Section data is 0.58. Additional section text is: FCJDDDMNLBUSJMCZVSBPYWCKSFJEARBXXFPAGBTKCWKHPEDGYWYTNGLVGQGJAFZRUMNSDCHKTTMGRFNSUZKFLOUGNWHUBNLVMGDB.

This is section D

Section data is 0.52. Additional section text is: YQIXHABFVQUAAYZNWTZXJDISSLTZJJAZOLJMJSXEENFTUOFOTYKDNNUMFDXLJSWZEVDLCLSYCTSMEXFLBVQYRTBEVZLCTEBPUGTT.

Answer 2

Just sharing the approach I've used eventually.

I wrote a markdown file for the section. prepared the data for each section in the master document, and looped over all the sections I needed, each time calling to knit_child() with the section Rmd.

Answer 3

I know this is late, but I used this in my code to make numbered sections and it works a treat.

for (k in 1:length(listcsv)){ #Begin Loop at pdf file one and continue until all have been completed
subsection <- paste("5", k, sep = ".")}

this uses the loop number (k) to create the subsection number and then paste it against the section number. This happens to be in section 5, but you could use the same principle to make sections and subsections ad infinitum.

Answer 4

A late answer building an example on @amit 's answer about the use of knit_child(). According to knitr documentation it is possible to do something like what was asked by:

1. Setting output of the chunk to as-is.
2. Set possible variables accessed in the child document before calling knitr_child(), as once rendered, the environment for the child is the same as the parent. This is the only way I found to kind of "pass parameters" to the child, but maybe there is a more elegant way to do this.
3. Storing your knitr_child() outputs in a list.
4. Use cat to print them all right after the other.

I have done this using Quarto but I think it should work just the same, as knitr was built to work on Rmarkdown.

A small reproducible example:

If your child document child.qmd looked like this:

---
tag: "Child document"
title: "Child document"
---

## `r child_section_title`

This section changes title according to what `child_section_title` value
is in the main markdown document.

You could render multiple differently titled chunks on your main .qmd file doing something like:

```{r, results='asis'}
knit_child_with_params <- function(p) {
  child_section_title <- p
  knitr::knit_child(
    "child.qmd",
    envir = environment(),
    quiet = TRUE)
}

# This needs to be declared outside the function
child_section_title <- ""
title_list <- list("Section title 1",
                   "Another title",
                   "Some other thing")

res <- lapply(title_list, knit_child_with_params)

cat(unlist(res), sep = '\n')

Think about keeping your child document chunks unnamed if you are going to do this, otherwise repeated names will make the rendering crash.

Answer 5

I came upon this question, looking to do the same. However I found the answers didn't work.

I generated this which works for my script, taking some of the comments above. It dynamically generates the \subsection headers in LaTeX and neatly produces the subchapters in the final pdf document.

I used the following as chunk header:

{r Automated, echo=FALSE, background=NA, comment=NA, results = 'asis'}

for (i in YourData) {

  # add a subsection title for the LaTeX report
  subsection_title <- paste("\\subsection{ The name of your chapter ", i ,"}")
  cat(subsection_title, "\n")

  # Rest of your code to include in chapter...

}