File Upload

Learning Objectives

• Learn how to upload datasets for use in the Shiny App.
• Chapter 8 of Mastering Shiny.
• Shiny Cheatsheet.
• Optional Resources
  • Shiny Tutorial.
  • Shiny Examples.

Static Dataset Upload

• If your Shiny app is designed to analyze only a single dataset (which might contain multiple files), then you should upload it at the start of the app.

  1. Create a new “data” folder in your app.
  2. Place all data files in the “data” folder.
  3. Read in these data at the start of the app.

• New data folder:

   

• Put data in data folder:

   

• Load data at beginning of app:

  library(shiny)
  library(readr)
  estate <- read_csv("./data/estate.csv")
  
  ui <- fluidPage(
    tableOutput("estate")
  )
  
  server <- function(input, output, session) {
    output$estate <- renderTable({
      head(estate)
    })
  }
  
  shinyApp(ui, server)

• When a Shiny app is run, the location of “app.R” is the location of the working directory, so all file upload/download must be done from that location as a reference point.

Interactive File Upload

• Use the fileInput() function in the UI to allow users to choose the source of the dataset.

  library(shiny)
  
  ui <- fluidPage(
    fileInput("file", "Where is the file?")
  )
  
  server <- function(input, output, session) {
  
  }
  
  shinyApp(ui, server)

   

• In the server() function, the element in input (in this case input$file) is a data frame with the following columns:

  • name: The name of the file on the user’s computer.

  • size: The size of the file in bytes. Shiny only accepts files up to 5 MB. To increase it to 10 MB, type the following somewhere in “app.R”:

    options(shiny.maxRequestSize = 10 * 1024^2)

  • type: The file extension (text/csv, text/plain etc)

  • datapath: A temporary path file.

• Useful arguments:

  • accept: What file extensions are acceptable (".csv", ".txt", etc).
  • buttonLabel: Customize label of button.
  • multiple: Can the user upload multiple files?

• Example Shiny App

  library(shiny)
  
  ui <- fluidPage(
    fileInput("upload", NULL, buttonLabel = "Upload...", multiple = TRUE),
    tableOutput("files")
  )
  
  server <- function(input, output, session) {
    output$files <- renderTable(input$upload)
  }
  
  shinyApp(ui = ui, server = server)

• General strategies:’

  • Place code to read in files inside a reactive() call.
  • Inside the reactive call, always use req() to wait to read in data until the path is available.
  • Save the read-in files as reactive elements.
  • In the server function, you use the datapath value as the path argument in read_csv(), read_tsv(), readRDS(), etc.

  library(shiny)
  library(readr)
  
  ui <- fluidPage(
    fileInput("file", "What file?", accept = "text/csv"),
    tableOutput("head")
  )
  
  server <- function(input, output, session) {
    data <- reactive({
      req(input$file)
      read_csv(input$file$datapath)
    })
  
    output$head <- renderTable({
      head(data(), 5)
    })
  }
  
  shinyApp(ui, server)