Create RMarkdown chuncks in a loop - r

Question

I would like to be able to create RMarkdown chuncks in a loop. I have tried doing this through a for loop, without much success. I imagine this could probably be possible through lapply, as one would do for creating UIs in a shiny app. However, I haven't had any success so far.
Reprex:
---
title: "Untitled"
output:
html_document:
theme: united
highlight: tango
toc: true
toc_float:
collapsed: false
smooth_scroll: false
---
```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = FALSE, message = FALSE, warning = FALSE)
```
```{r}
library(dplyr)
library(ggplot2)
df <- datasets::iris %>%
dplyr::as_tibble()
```
## setosa
```{r}
df %>%
dplyr::filter(Species == "setosa") %>%
ggplot2::ggplot(ggplot2::aes(Sepal.Length, Petal.Length)) +
ggplot2::geom_point()
```
## versicolor
```{r}
df %>%
dplyr::filter(Species == "versicolor") %>%
ggplot2::ggplot(ggplot2::aes(Sepal.Length, Petal.Length)) +
ggplot2::geom_point()
```
## virginica
```{r}
df %>%
dplyr::filter(Species == "virginica") %>%
ggplot2::ggplot(ggplot2::aes(Sepal.Length, Petal.Length)) +
ggplot2::geom_point()
```
My goal is to create the headings (setosa, versicolor, and virginica) and the chuncks with a loop.
For example:
for(i in c("setosa", "versicolor", "virginica")) {
## i
df %>%
dplyr::filter(Species == i) %>%
ggplot2::ggplot(ggplot2::aes(Sepal.Length, Petal.Length)) +
ggplot2::geom_point()
}
Any ideas on how accomplish this?

Answer 1

If you want to create headings + outputs within a loop, you can do:
```{r species_loop, results='asis'}
for(i in c("setosa", "versicolor", "virginica")) {
cat(paste0("\n\n## ", i, "\n"))
p <- df %>%
dplyr::filter(Species == i) %>%
ggplot2::ggplot(ggplot2::aes(Sepal.Length, Petal.Length)) +
ggplot2::geom_point()
print(p)
}
```
So:
Using results='asis' to allow output that you cat() to be interpreted as Markdown syntax
cat()ing the required markdown syntax to produce the headers (surrounded by some newlines to make sure it's interpreted properly)
Explicitly print()ing the plot within the loop.

Answer 2

A function based on cat would replicate your chunks for every iris species. For the one-time chunks use single cats.
FUN <- function(x) cat("\n##", x, "
```{r}
df %>%
dplyr::filter(Species == ",x, ") %>%
ggplot2::ggplot(ggplot2::aes(Sepal.Length, Petal.Length)) +
ggplot2::geom_point()
```\n")
To produce the shown .Rmd file, you could use sink. (For sake of brevity I'll omit the header here.)
sink(file="iris.Rmd") ## start `sink`
cat("```{r}
library(dplyr)
library(ggplot2)
df <- datasets::iris %>%
dplyr::as_tibble()
```")
invisible(sapply(c("'setosa'", "'versicolor'", "'virginica'"), FUN))
sink() ## end `sink`
You'll find your .Rmd file in your working directory (getwd()).