How to conditionally set a reactive value with fileInput?

Question

I'm trying to upload either a csv file or an rds file and use it as the dataset for creating a table. I tried using a conditional if/else, but I'm getting this error: argument is of length zero. I would like to upload it outside of the renderTable as I like to use the reactive dataset for other purposes too.

Code

library(shiny)

ui <- fluidPage(

    sidebarLayout(
        sidebarPanel(
            fileInput("file_csv", "Choose CSV File", accept = ".csv"),
            checkboxInput("header", "Header", TRUE),
            fileInput("file_rds", "Choose RDS File", accept = ".rds"),
        ),

        mainPanel(
           tableOutput("table1")
        )
    )
)

server <- function(input, output) {

    dataset <- reactive({
        if(input$file_csv) {
            file <- input$file_csv
            ext <- tools::file_ext(file$datapath)
            
            req(file)
            validate(need(ext == "csv", "Please upload a csv file"))
            
            read.csv(file$datapath, header = input$header)
        } else {
            readRDS(file_rds$datapath)
        }
    })
    
    output$table1 <- renderTable({
        head(dataset())
    })
}

shinyApp(ui = ui, server = server)

Attempt with observeEvent (not working):

    output$table1 <- renderTable({
        req(dataset())
        head(dataset())
    })
    
    observeEvent(input$file_csv, {
        dataset <- read.csv(input$file_csv$datapath, header = input$header)
    })
 
    observeEvent(input$file_rds, {
        dataset <- readRDS(input$file_rds$datapath)
    })
      

Attempt at rds file (not working):

       if(!is.null(input$file_rds )) {
            
            file <- input$file_rds
            req(file)
            
            readRDS(file$datapath)
            
            }

Answer 1

We can use

server <- function(input, output) {
  
  dataset <- reactive({
    req(input$file_csv)
    if(!is.null(input$file_csv )) {
      file <- input$file_csv
      ext <- tools::file_ext(file$datapath)
      
      req(file)
      validate(need(ext == "csv", "Please upload a csv file"))
      
      read.csv(file$datapath, header = input$header)
    } else {
      readRDS(input$file_rds$datapath)
    }
  })
  
  output$table1 <- renderTable({
    head(dataset())
  })
}

• output

-validation check