Shiny App Structure Cheatsheet: Essential Quick Reference

Shiny App Structure

Essential patterns and code snippets for rapid Shiny development

1 Basic App Structure

# Essential app.R structure
library(shiny)

# UI: What users see
ui <- fluidPage(
  titlePanel("My App"),
  sidebarLayout(
    sidebarPanel(
      # Input controls here
    ),
    mainPanel(
      # Output displays here
    )
  )
)

# Server: What app does
server <- function(input, output) {
  # Reactive logic here
}

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

Quick Tip: Always save as app.R or use ui.R + server.R + global.R

2 Essential Input Controls

# Text input
textInput("name", "Enter name:")

# Numeric input
numericInput("num", "Number:", 
             value = 10, min = 1, max = 100)

# Slider
sliderInput("range", "Range:",
            min = 0, max = 100, value = 50)

# Select dropdown
selectInput("var", "Choose:",
            choices = list("A" = "a", "B" = "b"))

# Action button
actionButton("go", "Run Analysis")

Access Pattern

ìnput$name → Get text input value input$num → Get numeric input value input$go → Get button click count

3 Output Display Types

# UI side - what to display
plotOutput("myplot")
tableOutput("mytable")
textOutput("mytext")
verbatimTextOutput("mycode")

# Server side - how to create
output$myplot <- renderPlot({
  plot(cars)
})

output$mytable <- renderTable({
  head(cars)
})

output$mytext <- renderText({
  paste("Hello", input$name)
})

Remember: UI functions end with Output, server functions start with render

4 Reactive Programming

# Reactive expression
filtered_data <- reactive({
  cars[cars$speed > input$min_speed, ]
})

# Use reactive data
output$plot <- renderPlot({
  plot(filtered_data())  # Note the ()
})

# Observer (side effects)
observe({
  print(paste("Speed changed to:", input$min_speed))
})

# Event reactive (triggered by button)
analysis_result <- eventReactive(input$go, {
  # Expensive computation here
  lm(dist ~ speed, data = cars)
})

Reactive Flow

Input Changes → Reactive Expressions Update → Outputs Re-render

5 Common Layout Patterns

# Sidebar layout
sidebarLayout(
  sidebarPanel(# Controls),
  mainPanel(# Results)
)

# Tabbed layout
tabsetPanel(
  tabPanel("Plot", plotOutput("plot")),
  tabPanel("Table", tableOutput("table"))
)

# Grid layout
fluidRow(
  column(4, # Input column),
  column(8, # Output column)
)

Mobile Tip: Use fluidPage() for responsive design that works on all devices

6 File Organization

# Single file app
myapp/
  └── app.R

# Multi-file app
myapp/
  ├── ui.R          # UI definition
  ├── server.R      # Server logic
  ├── global.R      # Shared objects
  └── www/          # Static files
      ├── style.css
      └── logo.png

# Production app
myapp/
  ├── R/            # R functions
  ├── data/         # Data files
  ├── www/          # Web assets
  └── app.R

Best Practice

Use global.R for data loading and function definitions shared by UI and server

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