Possible to use knitr cache chunk in interactive rmarkdown doc?

9
votes

I've noticed that when I have an Rmd with runtime: shiny in the YAML, code chunks don't seem to be read from cache. I'm wondering if using the shiny engine for rmarkdown just doesn't support chunk caching, or am I doing something wrong?

Example Rmd file:

---
title: "Cache test"
output: html_document
---

```{r cache=TRUE}
Sys.sleep(10)
```

If you run this 5 times, only the first time will take 10 seconds, and any subsequent run will be fast.

But if you add the runtime: shiny option to the YAML, then every single run will take 10 seconds.

(PS question: any better way to test whether or not code chunks cache is being used?)

1
rshinyknitrr-markdownshiny-server

1 Answers

2
votes

i ran into the same problem where, in runtime: shiny, the cache switch was ignored.

Nowadays there is a workaround, using runtime: shiny_prerendered and context="data" with cache=TRUE:

---
title: "Cache test"
output: html_document
runtime: shiny_prerendered
---

```{r,context="data", cache=TRUE}
Sys.sleep(10)
```

this behaves as expected; on the first run, rendering takes 10 seconds; on all subsequent runs, the cached chunk is used.