Mastering Shiny

Chapter 9. Uploads and Downloads

Transferring files to and from the user is a common feature of apps. You can use it to upload data for analysis or download the results as a dataset or as a report. This chapter shows the UI and server components that you’ll need to transfer files in and out of your app. We begin by loading shiny:

library(shiny)

Upload

We’ll start by discussing file uploads, showing you the basic UI and server components, and then showing how they fit together in a simple app.

UI

The UI needed to support file uploads is simple: just add fileInput() to your UI:

ui <- fluidPage(
  fileInput("upload", "Upload a file")
)

Like most other UI components, there are only two required arguments: id and label. The width, buttonLabel, and placeholder arguments allow you to tweak the appearance in other ways. I won’t discuss them here, but you can read more about them in ?fileInput.

Server

Handling fileInput() on the server is a little more complicated than other inputs. Most inputs return simple vectors, but fileInput() returns a data frame with four columns:

name

The original filename on the user’s computer.

size

The file size, in bytes. By default, the user can only upload files up to 5 MB. You can increase this limit by setting the shiny.maxRequestSize option prior to starting Shiny—to allow up to 10 MB run options(shiny.maxRequestSize = 10 * 1024^2), for example.

type

The “MIME type” of the file.¹ This is a formal specification of the file type that ...