Render rmarkdown to character variable - r

Question

I am fairly new to R markdown. I have built an app that requires the user to provide multiple inputs to generate a table, which can then be saved locally.
I have been now asked to implement a sort of report to list all the variables inserted by the user (in a sort of formatted document), so that before generating the table one can review all the settings and change them in case of errors.
To avoid major UI restructure, I thought about using a r markdown document and visualize it inside a modal. My problem is that rmarkdown::render renders to an output, while bs_modal takes for the argument body a character (HTML) variable.
Is there a way to make this work? Or are there better way to accomplish this?
A minimal example:
my .Rmd
---
title: "Dynamic report"
output:
html_document: default
pdf_document: default
params:
n : NA
---
A plot of `r params$n` random points.
```{r, echo=FALSE}
plot(rnorm(params$n), rnorm(params$n))
```
My App.R
library(shiny)
library(bsplus)
library(rmarkdown)
shinyApp(
ui = fluidPage(
selectInput(
inputId = "numb",
label = "Label with modal help",
choices = 50:100
),
actionButton(inputId = "mysheet",
label = "Open modal") %>% bs_attach_modal(id_modal = "modal1"),
textOutput("result")
),
server = function(input, output) {
observeEvent(input$mysheet, {
params <- input$numb
md_out <-
rmarkdown::render(
"report.Rmd",
params = params,
envir = new.env(parent = globalenv())
)
bs_modal(
id = "modal1",
title = "Equations",
body = md_out,
size = "medium"
)
})
output$result <- renderText({
paste("You chose:", input$numb)
})
}
)

Answer 1

bs_modal does not work like this, it must be in the UI. Below is a solution using the classical Shiny modal, no bsplus or other package.
library(shiny)
shinyApp(
ui = fluidPage(
selectInput(
inputId = "numb",
label = "Label with modal help",
choices = 50:100
),
actionButton(inputId = "mysheet",
label = "Open modal"),
textOutput("result")
),
server = function(input, output) {
observeEvent(input$mysheet, {
params <- list(n = input$numb)
md_out <-
rmarkdown::render(
"report.Rmd",
params = params,
envir = new.env(parent = globalenv())
)
showModal(modalDialog(
includeHTML(md_out),
title = "Equations",
size = "m"
))
})
output$result <- renderText({
paste("You chose:", input$numb)
})
}
)
Use html_fragment as the Rmd output:
---
title: "Dynamic report"
output:
html_fragment
params:
n : NA
---
A plot of `r params$n` random points.
```{r, echo=FALSE}
plot(rnorm(params$n), rnorm(params$n))
```