how to use a for loop in rmarkdown?

Question

Consider this simple example:

---
title: "Untitled"
output: ioslides_presentation
---

```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = FALSE)
```
## Slide with R Output
```{r t,  warning=FALSE, message=FALSE}

library(knitr)
library(kableExtra)
library(dplyr)

for(threshold in c(20, 25)) {
  cars %>% 
    filter(dist < threshold) %>%
    kable('html') %>% 
    kable_styling(bootstrap_options = "striped") 
}
```

Here I simply want to print each output of the for loop into a different slide. In this example, there are two calls to kablethat should go on two different slides.

The code above does not work. Am I even using the right packages for that? Any ideas?

Thanks!

Answer 1

You can use the asis option:

---
title: "Untitled"
output: ioslides_presentation
---

```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = FALSE)
library(knitr)
library(kableExtra)
library(dplyr)
# needed so r will include javascript/css dependencies needed for striped tables:
kable(cars, "html") %>% kable_styling(bootstrap_options = "striped")
```

```{r, results = "asis"}
for (threshold in c(20, 25)) {
  cat("\n\n##\n\n")
  x <- cars %>%
    filter(dist < threshold) %>%
    kable('html') %>%
    kable_styling(bootstrap_options = "striped")
  cat(x)
}
```

Answer 2

Here's the start of a solution. You can print strings with markdown, either by making the strings yourself or using pander's pandoc.* functions. If you set results="asis" for that chunk, it will get compiled the same as any other markdown. I used cat to make the ## headings, but commented out two pander functions that you could try also to make headers or horizontal rules to split slides.

There's more detail on the pander functions here, plus other SO questions such as this one.

---
title: "Untitled"
output: ioslides_presentation
---

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

library(knitr)
library(kableExtra)
library(dplyr)

```


```{r, results='asis'}
for(threshold in c(20, 25)) {
  # pander::pandoc.header(sprintf("Threshold = %s", threshold))
  # pander::pandoc.horizontal.rule()
  cat(paste("\n##", "Threshold =", threshold), "\n")

  tbl <- cars %>% 
    filter(dist < threshold) %>%
    kable(format = "html") %>%
    kable_styling(bootstrap_options = "striped")
  print(tbl)
}
```

One issue is that when I knit this, I'm not getting the striped table that you'd expect. If I add a slide before this chunk and put a table in it with these kableExtra settings, I do get stripes, but the first table is also pretty ugly...I'm not sure if that's a bug or conflicting CSS somewhere or what.

Answer 3

To get rid of that bogus table, you can try to put options(kableExtra.html.bsTable = T) in your setup section.