Short Course on R Tools

Building Interactive Web Apps with Shiny

Mehdi Maadooliat and Hossein Haghbin

Marquette University
SCoRT - Summer 2025

Outline

• Introduction to Shiny
• App Structure: UI & Server
• Inputs & Outputs
• Shinyapps Gallery
• Reactivity, Isolate & Observer
• Deployment & Best Practices
• Hands-on Exercises

Introduction to Shiny

• What is Shiny?

  • R package for interactive web apps

  • No web dev expertise needed

• When to use: dashboards, interactive reports, teaching tools

• Tutorial sources:

  • RStudio official tutorial

  • Mastering Shiny by Hadley Wickham

• 🔗 Launch R: run shiny::runExample("01_hello").

Structure of a Shiny App

# app.R single-file app
library(shiny)
ui <- fluidPage(
  ...
)

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

shinyApp(ui, server)

• ui defines layout and inputs/outputs

• server contains R code & reactivity

Structure of a Shiny App

# app.R single-file app
library(shiny)
ui <- fluidPage(
  titlePanel("Hello Shiny"),
  sidebarLayout(
    sidebarPanel(sliderInput("obs", "Observations:", 1, 100, 50)),
    mainPanel(plotOutput("distPlot"))
  )
)

server <- function(input, output) {
  output$distPlot <- renderPlot({
    hist(rnorm(input$obs))
  })
}

shinyApp(ui, server)

• ui defines layout and inputs/outputs

• server contains R code & reactivity

Structure of a Shiny App

Shiny apps come in two parts:

UI

• Defines the layout and appearance.

• Contains elements such as:

  • layout structures (sidebars)
  • inputs (text boxes, sliders, buttons)
  • outputs (plots, tables)

Server

• Performs calculations.

• Contains the logic to respond to user inputs, and update outputs.

• Communicates with the UI to dynamically render outputs.

Shinyapps Gallery

🔗 Launch R: File > New File > Shiny Web App…

Exercise

05:00

• Open up your IDE of choice.

• Make sure you have the {shiny} package installed.

• Create an app.R file.

• Add ui and server elements, as well as shiny::shinyApp(ui, server).

• Check it works.

Shinyapps Gallery

Inputs & Outputs

• Inputs: textInput(), selectInput(), sliderInput(), etc.

• Outputs: renderPlot(), renderTable(), renderUI(), etc.

• Binding: output objects referenced by output$...

input$slider  # numeric
input$check   # logical

Widgets - Input

Widgets - Output Table

🔗 </> VIEW CODE

Reactivity Fundamentals

• Reactive expressions: cache results

  rv <- reactive({ rnorm(input$obs) })
  output$plot <- renderPlot(hist(rv()))

• isolate(): break reactive chain

  output$summary <- renderText({
    paste0('input$text is "', input$text,
    '", and input$n is ', isolate(input$n))
  })      

• Observers: side-effect actions

  observeEvent(input$go, { showModal(...) })

Reactivity Demo

Isolate Demo

Observers Demo

Deploying a Shiny app

• What do we mean by deployment?

  • Getting the Shiny app off your laptop and out into the world!

• Traditional deployment

• We need a server to run the R code:
  • shinyapps.io
  • Posit Connect
  • Private server (e.g. university)

Shinylive deployment

Shinylive deployment

See posit-dev.github.io/r-shinylive.

The {shinylive} package converts a standard shiny app into a shinylive app:

install.packages("shinylive")

Assuming your app.R file is in a folder called app:

shinylive::export("app", "site")

You can then use the files in the site folder to deploy it as a normal website.

*not all R packages are available for shinylive.

**initial load time is still quite slow.

Tips for building Shiny apps

• Build tests using shinytest2.

• Building apps as packages helps with dependency management.

• Learn a little bit of HTML, CSS, and Javascript.

• Modules are a good way to reuse bits of UI and server code across the application.

• Start with pen and paper… (think about user experience!)

Hands-on Exercises (30 min)

• KNN Regression via shiny

Resources & Further Reading

• RStudio tutorial: shiny.rstudio.com/tutorial

• Mastering Shiny: mastering-shiny.org

• ShinyUiEditor: rstudio.github.io/shinyuieditor

• Shiny for Python: shiny.posit.co/py

• shinythemes: rstudio.github.io/shinythemes

• shinylive examples: shinylive.io/r/examples/

• Examples: github.com/rstudio/shiny-examples/

Q&A

Thank You

• Happy coding with Shiny!