Is there an equivalent to the Shiny fileInput function for saving outputs?

Question

Shiny has a nice fileInput() function for allowing the user to browse directories and select the file to upload into the App. Extracted from https://shiny.rstudio.com/reference/shiny/1.7.0/fileInput.html, here's the MWE:

ui <- fluidPage(
  sidebarLayout(
    sidebarPanel(
      fileInput("file1", "Choose CSV file to upload", accept = ".csv"),
      checkboxInput("header", "Header", TRUE)
    ),
    mainPanel(
      tableOutput("contents")
    )
  )
)
  
server <- function(input, output) {
  output$contents <- renderTable({
    file <- input$file1
    ext <- tools::file_ext(file$datapath)
      
    req(file)
    validate(need(ext == "csv", "Please upload a csv file"))
  
    read.csv(file$datapath, header = input$header)
  })
}
  
shinyApp(ui, server)

I'm using this in my App for retrieving data, I really like it. However, I'm looking for a similar feature where the user can save a dataframe that results from running the App in a similar way, by browsing directories to choose a location to save the file and selecting a file name. Key is the ability to browse local directories. Any ideas how to accomplish this? Preferably in a way as simple as fileInput().

Files will be .csv, though I'm thinking about .xls too.

Usually this is done with a downloadButton. After pressing the button the browser allows the user to select a directory and a filename. — ismirsehregal
– ismirsehregal, Commented Nov 18, 2021 at 12:38

bird · Accepted Answer · 2021-11-18 12:38:56Z

You can use downloadButton in ui and downloadHandler in server as follows:

library(shiny)

ui <- fluidPage(
        sidebarLayout(
                sidebarPanel(
                        fileInput("file1", "Choose CSV file to upload", accept = ".csv"),
                        checkboxInput("header", "Header", TRUE),
                        downloadButton("download")
                ),
                mainPanel(
                        tableOutput("contents"),
                )
        )
)

server <- function(input, output) {
        output$contents <- renderTable({
                file <- input$file1
                ext <- tools::file_ext(file$datapath)
                
                req(file)
                validate(need(ext == "csv", "Please upload a csv file"))
                
                read.csv(file$datapath, header = input$header)
        })
        
        output$download <- downloadHandler(
                filename = function() {
                        paste0(input$file1, ".csv")
                },
                content = function(file) {
                        write.csv(contents(), file)
                }
        )
}

shinyApp(ui, server)

This answer confused me for a moment. I don't get the file browser when I click on the download button. Then it occurred to me that I open my shiny apps in Chrome. If using the RStudio built-in browser, I get the file browser (I'm using Windows, for what it's worth). It seems some of these behaviors may be browser dependent (and possibly subject to group policy)

Benjamin · Accepted Answer · 2021-11-18 12:45:28Z

Here's a really basic example that invokes file.choose when you click on the action button.

library(shiny)

shinyApp(
  ui = 
    fluidPage(
      textInput(inputId = "txt_to_save", 
                label = "Enter text to save to a file"),
      actionButton(inputId = "btn_save_txt", 
                   label = "Save Text to File")
    ),
  
  server = 
    shinyServer(function(input, output, session){
      
      observeEvent(
        input$btn_save_txt, 
        {
          dest_file <- file.choose()
          write(input$txt_to_save, 
                dest_file)
        }
      )
      
    })
)

In practice, if you wanted to have the file name created by the application, but the directory chosen by the user, you could also use choose.dir().

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