Writing shiny apps

A Web server is needed to run shiny apps, shinyapps.io can be used for free (only up to 5 apps) or there is a way to create your own server called shiny server. https://rstudio.com/products/shiny/shiny-server/

Making a shiny app

You need to make a user interface (UI) and server instructions which tell the server what to do when inputs are changed. Both these instructions can be in the same document.

The UI generates html, for the web page, from R code

The two sections of code are then knitted together

Start with a template; in Rstudio you can choose ‘new file’, ‘Shiny Web App’

library(shiny)
ui <- fluidPage()

server <- function(input, output) {}

shinyApp(ui = ui, server = server)

Inputs: what people change

Outputs: what the user sees when they change inputs

To add elements to an app we add to fluidPage()

Adding input functions

• sliderInput for example generates some html code to display the code.

• Shiny provides a few input functions which can be used

• inputId = name for the input

• label = the label to display, which can be used to instruct users how to use the input

We can use the values stored in our input using input$inputID. This is useful for when we are formatting the output, we can make the output depend on the input

Output

Save the output which we want to build to output$hist for example

Build the output with the render function (helps assemble the code into html)

Access input values with input$

Reactivity

When inside a render function such as renderPlot the code is reactive (reacts to changes in the input variables)

Saving the app for sharing

Save into one directory with app.R as the app name, as well as datasets images etc needed to run the app

Posting to shinyapps.io

Sign up for an account on shinyapps.io. Follow all instructions their (install rsconnect, etc.)

Create a shiny app in rstudio.

Then you can publish straight to shinyapps.io (see below image). Make sure to publish all the files needed to run the R script inside the app

Code for embedding video shiny:

### Code for embedding video
  library(shiny)
  ui <- fluidPage(
      HTML('')
  )
  server <- function(input, output, session) {
  }
  #shinyApp(ui, server)

Code for question and answer shiny:

### Code for question and answer
  library(shiny)
  ui <- fluidPage(
      radioButtons("rb", "What is quantity demanded  equal to?",
                         choiceNames =
                             list("None selected", "Supply", "quantity demanded",
                                  "Price", "quantity supplied"),
                         choiceValues =
                             list("", "supply", "quantity demanded", "price", "quantity"),
                   selected = ""
      ),
      textOutput("txt")
      )
  server <- function(input, output) {
      output$txt <- renderText({
          if (input$rb == "supply"){
              print("You are correct")
              } else if (input$rb == ""){
                  print("")}
                  else{
                      print("You are incorrect")}
              })
  }
  #shinyApp(ui, server)