How to update shiny controls in dynamic rmarkdown document?

[chris warth]

Is there any way to update the contents of a selectInput control inside an rmarkdown document?

For example, in the document below I would like the selectInput for B to have different choices depending on the value chosen for A.

It almost looks like one could use updateSelectizeInput(), but that takes a 'session' argument which I don't see exposed in rmarkdown.

Any ideas?

---
title: "An Empty Document"
output: html_document
runtime: shiny
---
This space intentionally left blank.
```{r eval=TRUE, echo=FALSE}
inputPanel(
    selectInput("A", "Control A:",  choices = c("A", "B", "C")),
    selectInput("B", "Control B:",  choices = c("1", "2", "3")),
    selectInput("C", "Control C:",  choices = NULL)
)

```
```{r eval=TRUE, echo=FALSE}

reactive({
    if (input$A == "B") {
        # I would like to update the choices for selectInput B here.
    }
})
```

[Vincent]

I haven't used shiny in rmarkdown at all yet but ... can you use renderUI? In a regular Shiny app, within renderUI you can do a check for the value of input$A and then adjust the values available to B (which could be only one value).

[Joe Cheng]

You can use updateSelectInput, the "session" is available implicitly. But you need to use observe, not reactive. So this:

reactive({
    if (input$A == "B") {
        # I would like to update the choices for selectInput B here.
    }
})

should be:

observe({

    if (input$A == "B") {

        updateSelectInput(session, "B", choices = ...)
    }
})

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[chris warth]

renderUI() did not seem to have any effect inside of an rmarkdown document, whereas it works fine for me inside of a traditional shiny app.

- Chris

[Joe Cheng]

It should work--in fact the entire runtime:shiny mechanism is based on a big renderUI call. Any chance you can provide the code you tried?

On Tue, Oct 14, 2014 at 4:35 PM, chris warth <csw...@gmail.com> wrote:

renderUI() did not seem to have any effect inside of an rmarkdown document, whereas it works fine for me inside of a traditional shiny app.

- Chris

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