Examples

See the following gallery of Shiny example from Posit: https://shiny.posit.co/r/gallery/

A simple Shiny App

Put the following into a Shiny App using File \(\rightarrow\) New File \(\rightarrow\) Shiny Web App ... as a file called app.R.

library(shiny)

ui <- fluidPage(
  "Hello, world!"
)

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

shinyApp(ui, server)

How to run a Shiny App?

What does it look like?

Back in R…

Go back and look at the console. You will see something like:

Listening on http://127.0.0.1:7521

R is busy! It is running your Shiny App. You can’t do anything in R because the processes are engaged with the Shiny App.

Pieces

Shiny applications will be contained in one app.R file. The file contains two key components:

ui: code for the user interface. The user interface is the webpage that your user will interact with.

server: code for the computer part. What should the computer/server do with your inputs as the user changes them.

The last code at the bottom, shinyApp(ui = ui, server = server), will compile everything together to result in the interactive webpage.

Press Run App at the top of RStudio and see what happens!

Pieces

library(shiny)

shinyApp(
  ui = list(
    # new (to you) widgets go here
  ),
  
  server = function(input, output, session) {
    # somewhat familiar (to you) code goes here
  }
)

A brief widget tour

https://rundel.shinyapps.io/widgets/

The default Shinny App

#
# This is a Shiny web application. You can run the application by clicking
# the 'Run App' button above.
#
# Find out more about building applications with Shiny here:
#
#    https://shiny.posit.co/
#

library(shiny)
library(tidyverse)

# Define UI for application that draws a histogram
ui <- fluidPage(

    # Application title
    titlePanel("Old Faithful Geyser Data"),

    # Sidebar with a slider input for number of bins 
    sidebarLayout(
        sidebarPanel(
            sliderInput("bins",
                        "Number of bins:",
                        min = 1,
                        max = 50,
                        value = 30)
        ),

        # Show a plot of the generated distribution
        mainPanel(
           plotOutput("distPlot")
        )
    )
)

# Define server logic required to draw a histogram
server <- function(input, output) {

    output$distPlot <- renderPlot({
        faithful |> 
           ggplot(aes(x = waiting)) + 
              geom_histogram(bins = input$bins,
                             fill = "darkgrey",
                             color = "white")  +
              labs(x = "Waiting time to next eruption (in mins)",
                   title = "Histogram of waiting times",
                   y = "") + 
              theme_minimal()
    })
}

# Run the application 
shinyApp(ui = ui, server = server)

Running Old Faithful

• Run in RStudio

• See the app in action here: https://shiny.posit.co/r/gallery/start-simple/faithful/

reactive()

The function reactive() is worth pointing out. It is used to create a reactive expression — an expression that is automatically recalculated when any of its inputs change.

Use reactive() when

• You want to perform calculations that depend on user input and automatically update when those inputs change.
• You need to pass dynamically calculated values to other parts of the app (outputs, observers, etc.).
• You need to create reactive data or state, such as subsets or transformations of input data.

Do not use reactive() within any of the render*() functions because they are inherently reactive already!

Live demo

Let’s build a weather app! See sample files here: https://github.com/hardin47/ds002r-fds/tree/main/Shiny_weather

Shiny in Python

Check it out!

https://shiny.posit.co/py/