What's the correct way to structure a Shiny project with a downloadable RMarkdown report?

shiny
,
1

[Cross-posting from SO:]
I have a reasonably complex Shiny App (several modules) that allows users to fiddle with many different parameters and generate a lot of plots. I want to add the ability for users to download the output they've generated in the Shiny App as a reproducible RMarkdown.

I have read through Shiny - Generating downloadable reports and understand how to do this with a separate Rmarkdown file. However, all of my plotting/data manipulation code is in the Shiny app and it seems like poor practice (violation of DRY) to copy it over to an RMarkdown file -- then any time I want to change the plotting code I would need to change it twice.

What's the correct way to do this so that I don't have to maintain two sets of the same code?

2

refactor your plotting code

output$plotname <- renderPlot({
... lots of plotting code ...
}}

-->>

plotname_content <- reactive({
... lots of plotting code ...
})
output$plotname <- renderPlot({
     req(plotname_content())
}}

Thereafter you can continue to use the proposed method of generating downloadable results, but you pass plotname_content as a parameter to your rmarkdown

1 Like
3

@nirgrahamuk that's helpful, thanks. One small issue with that is that my plot is the result of a promise:
This is essentially my server.R:

plotname_content <- reactive({
  future_promise({
     data %>% 
        slow_transform()
  }) %...>% {
    plot_data(.)
  }
})
output$plotname <- renderPlot({
     req(plotname_content())
}}

But then the generated rmarkdown looks like:

Results
Overview
## <Promise [fulfilled: gg]>
4

There's a lot left out of your post.
I would simply expect that if renderPlot can plot plotname_content() then it could be passed as a parameter. in the equivalent manner to anywhere else.
What happens when you remove the promise layer ? does the markdown work, or give another error ? if the latter then the issue isnt with the promise but with the parameter passing...

5

Removing the promise works just fine (markdown renders correctly) -- this goes back to my original point: it seems like there's not a great way to share code between Shiny and Markdown. Passing the reactive variable containing the plot seems like a good idea, but is failing in a reasonably common usecase (I imagine that many Shiny apps employ promises)

6

Perhaps see if this hold function can be used on the markdown side to wait on evaluation of the promise ?

7

That helped, thanks! I was able to solve my specific issue, but I remain a bit unsatisfied by the larger meta-answer.

8

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