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Shiny Cheat Sheet

A comprehensive cheat sheet covering essential Shiny concepts, functions, and best practices for building interactive web applications with R.

Core Concepts

Basic Structure

A Shiny app consists of two main parts: a user interface (ui) and a server function (server).

library(shiny)

ui <- fluidPage(
  # UI elements go here
)

server <- function(input, output) {
  # Server logic goes here
}

shinyApp(ui = ui, server = server)

The ui defines the layout and appearance of the app. It uses functions like fluidPage, sidebarLayout, and various input/output elements.

The server function contains the logic that makes the app interactive. It uses input to access values from the UI and output to render content.

UI Elements

fluidPage()

Creates a fluid layout that adapts to different screen sizes.

sidebarLayout()

Creates a layout with a sidebar and a main panel.

sidebarPanel()

Contains the elements in the sidebar.

mainPanel()

Contains the main content of the app.

titlePanel()

Adds a title to the page.

br()

Adds a line break.

Reactivity

Shiny uses a reactive programming model. When an input value changes, Shiny automatically re-executes the code that depends on that value.

reactive(): Creates a reactive expression that only re-evaluates when its dependencies change.

observe(): Executes code in response to reactive changes, but doesn’t return a value.

observeEvent(): Executes code only when a specific event occurs (e.g., a button click).

Input Components

Common Input Widgets

textInput(inputId, label, value = "")

Creates a text input box.

numericInput(inputId, label, value, min = NA, max = NA, step = NA)

Creates a numeric input box with optional min, max, and step.

sliderInput(inputId, label, min, max, value, step = NULL)

Creates a slider input.

selectInput(inputId, label, choices, selected = NULL, multiple = FALSE)

Creates a dropdown select box.

radioButtons(inputId, label, choices, selected = NULL)

Creates a set of radio buttons.

checkboxGroupInput(inputId, label, choices, selected = NULL)

Creates a group of checkboxes.

checkboxInput(inputId, label, value = FALSE)

Creates a single checkbox.

dateInput(inputId, label, value = NULL, min = NULL, max = NULL, format = "yyyy-mm-dd", language = "en")

Creates a date input.

fileInput(inputId, label, multiple = FALSE, accept = NULL, width = NULL, buttonLabel = "Browse...", placeholder = "No file selected")

Creates a file upload input.

Output Components

Rendering Outputs

renderPlot()

Renders a plot (e.g., from ggplot2).

renderTable()

Renders a static table (e.g., from a data frame).

renderDataTable()

Renders an interactive table (using DataTables library).

renderText()

Renders text output.

renderPrint()

Renders the output of print().

renderUI()

Renders arbitrary HTML or Shiny UI elements. Useful for dynamic UIs.

Displaying Outputs in UI

plotOutput(outputId, width = "100%", height = "400px")

Displays a plot rendered by renderPlot().

tableOutput(outputId)

Displays a table rendered by renderTable().

dataTableOutput(outputId)

Displays an interactive table rendered by renderDataTable().

textOutput(outputId, inline = FALSE)

Displays text rendered by renderText().

verbatimTextOutput(outputId, placeholder = FALSE)

Displays text (verbatim) rendered by renderPrint().

uiOutput(outputId)

Displays UI elements rendered by renderUI().

Advanced Features

Download Handlers

Use downloadHandler() to create download buttons. Specify the filename and the content to be downloaded.

downloadButton("downloadData", "Download")

server <- function(input, output) {
  output$downloadData <- downloadHandler(
    filename = function() { paste("data-", Sys.Date(), ".csv", sep=") },
    content = function(file) {
      write.csv(data, file)
    }
  )
}

Session Management

The session object provides information about the user’s session and allows you to control the app’s behavior.

server <- function(input, output, session) {
  observe({
    # Update input values
    updateTextInput(session, "text", value = "New Value")
  })
}

JavaScript Integration

You can integrate JavaScript code into your Shiny apps using tags$script in the UI or by sending messages from R to JavaScript.

# UI
tags$script("alert('Hello from JavaScript!');")

Modules

Shiny modules allow you to encapsulate UI and server logic into reusable components. This promotes code organization and reusability.

# Define a module
myModuleUI <- function(id) {
  ns <- NS(id)
  tagList(
    textInput(ns("textInput"), "Enter text:"),
    textOutput(ns("textOutput"))
  )
}

myModuleServer <- function(id) {
  moduleServer(
    id,
    function(input, output, session) {
      output$textOutput <- renderText(input$textInput)
    }
  )
}

# Use the module in the main app
ui <- fluidPage(
  myModuleUI("myModule")
)

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