For loop in inside render UI

[pieterjanvc]

Hello,

I don't fully understand what your goal is, but I can give you a few pointers. I do recommend that you create a Shiny reprex so you can more easily show what's going on and have a 'working' example of the issue. This guide will help you create one:

Shiny debugging and reprex guide

Shiny issues can be challenging to resolve relative to other problems with your code or statistical methods. Shiny apps are often large, complex projects with interacting files. When seeking help from others it is considered polite to: First, do your best to work through RStudio's debugging tools to diagnose your issue on your own. Often those shiny logs and tracebacks are useful to others trying to help out. Second, strive to minimize the effort required to replicate your issue. You can do this with a reproducible example ("reprex"). Shiny Debugging Errors in Shiny code can be difficult to track down. If you don't know where your problem is coming from, you can track it down with some o…

If you only want to only filter on columns with factors, your first choices of selectInput "sel1" should only be those columns (so ColA and ColB). You can then have your selectInput "b" update its choices based on the choice of "sel1".

I created a dummy example to illustrate:

library(shiny)

ui <- fluidPage(
  selectInput("filter1","Variables",choices = c(),width = 150),
  selectInput("filter2","Variables",choices = c(),width = 150)
)

server <- function(input, output, session) {
  
  #Generate some data
  myData = data.frame(ColA = LETTERS[sample(1:5, 10, replace = T)], 
             ColB = LETTERS[sample(6:10, 10, replace = T)], 
             ColC= runif(10))
  
  #For filter 1, only use the columns with factors
  updateSelectInput(session, "filter1", 
                    choices = colnames(myData)[sapply(myData, class) == "factor"])
  
  #Based on filter 1, show the factors in filter 2
  observeEvent(input$filter1, {
    updateSelectInput(session, "filter2",
                      choices = myData[,input$filter1])
  }, ignoreInit = T)
  
}

shinyApp(ui, server)

NOTE: the ignoreInit = T for the second filter's observeEvent is needed to prevent an error occurring when there is nothing assigned yet to filter 1 when the app loads.

Again, if this is not answering your question, please create a reprex using the guide.

Kind regards,
PJ