Validating input file using shinyvalidate

shiny
1

I'm building an app that has an upload button. The button is a module, which I simplified for the purpose of the example here. I'd like to validate the input file using shinyvalidate, for example to ensure the file is a .csv. The logic of shinyvalidate lives outside of the upload module.

I can't seem to be able to access the actual file in the validation rule.

What's the recommended way to handle the validation in that case? Should I pass the validator to the module to perform the validation or is it possible to do it outside of the module?

Here's a simple app to illustrate what I'm trying to do.

library(shiny)
  
mod_upload_ui <- function(id, label = "Load data", ...) {
  ns <- NS(id)
  fileInput(
    ns("file"),
    label = label,
    buttonLabel = "Browse files",
    placeholder = "No files selected",
    ...
  )
}

mod_upload_server <- function(id) {
  moduleServer(id, function(input, output, session) {
    reactive(input$file)
  })
}

ui <- fluidPage(
  sidebarLayout(
    sidebar = sidebarPanel(
      mod_upload_ui("file")
    ),
    mainPanel(
      tableOutput("text")
    )
  )
)

server <- function(input, output, session) {
  iv <- shinyvalidate::InputValidator$new()
  
  # validate the input file
  iv$add_rule("file", function(x) {
    print(x) # prints NULL
  })
  
  iv$enable()
  
  file <- mod_upload_server("file")
  output$text <- renderTable({
    req(iv$is_valid())
    file()
  })
  
}

shinyApp(ui, server)
2

Part of the problem is that your fileInputid is file-file, not file because you have placed it inside the module. However if you use iv$add_rule("file-file" you get the error: Result of 'file-file' validation was not a single-character vector (actual class: data.frame) which seems to suggest that shinyvalidate isn't suitable to use with fileInput.

If you are just wanting to check it is a .csv then using accept = ".csv", in the fileInput goes a long way and you can double check by using tools::file_ext(input$file$datapath) == "csv" before trying to read the file. If there are more validation steps you want to do, it would be helpful to have more information about what they are.

3

Thanks for this.

Unfortunately, fileInput(accept =) doesn't seem to check the format of the file, at least when running the app locally.

I initially used the shinyFeedback package that I used inside the module to validate the file (in a similar fashion as you did with file_ext()) but I find it less convenient than shinyvalidate.

4

Just realized that fileInput(accept =) didn't work in my case because I didn't prefix the format with a dot… Using accept = "csv" doesn't work but accept = ".csv" does work.

5

Turns out I was wrong about shinyvalidate not being compatible. After some more fiddling (and some help from shiny assistant) here's an example:

library(shiny)

mod_upload_ui <- function(id, label = "Load data", ...) {
  ns <- NS(id)
  fileInput(
    ns("file"),
    label = label,
    buttonLabel = "Browse files",
    placeholder = "No files selected",
    accept = ".csv",
    ...
  )
}

mod_upload_server <- function(id) {
  moduleServer(id, function(input, output, session) {

    iv <- shinyvalidate::InputValidator$new()

    iv$add_rule("file", function(value) {
      if (is.null(value)) {
        return("Please upload a file")
      }

      if (tools::file_ext(value$name) != "csv") {
        return("Please upload a CSV file")
      }

      return(NULL)
    })

    iv$enable()

    list(file = reactive(input$file), valid = reactive(iv$is_valid()))
  })
}

ui <- fluidPage(
  sidebarLayout(
    sidebar = sidebarPanel(
      mod_upload_ui("file")
    ),
    mainPanel(
      tableOutput("text")
    )
  )
)

server <- function(input, output, session) {

  file_server <- mod_upload_server("file")
  output$text <- renderTable({
    req(file_server$valid())
    read.csv(file_server$file()$datapath)
  })

}

shinyApp(ui, server)
1 Like
6

Yep but in that case the validation is inside mod_upload_server(), which is ok but I wanted to keep it outside the module for flexibility purposes.

That said, you were right to point out that the correct id was file-file (and not file), so I could fix that to make it work in my example.

iv$add_rule("file-file", function(x) {
  if (!is.null(x) && tools::file_ext(x$name) != "csv") {
    "Must be a .csv file."
  }
})