Shiny for R :: Cheatsheet

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Building an App

A Shiny app is a web page (ui) connected to a computer running a live R session (server).

library(shiny)

Users can manipulate the UI, which will cause the server to update the UI’s display (by running R code).

Save your template as app.R. Keep your app in a directory along with optional extra files.

• app-name: The directory name is the app name
• app.R
• DESCRIPTION and README: (optional) used in showcase mode
• R/: (optional) directory of supplemental .R files that are sourced automatically, must be named R
• www/: (optional) directory of files to share with web browsers (images, CSS, .js, etc.), must be named www

Launch apps stored in a directory with runApp(<path to directory>).

To generate the template, type shinyApp and press Tab in the RStudio IDE or go to File > New Project > New Directory > Shiny Application.

# app.R 
library(shiny)

#In ui nest R functions to build an HTML interface
ui <- fluidPage(
  numericInput(inputId = "n", "Sample size", value = 25),
  plotOutput(outputId = "hist")
)
# Customize the UI with Layout Functions
# Add Inputs with *Input() functions
# Add Outputs with *Output() functions


# Tell the server how to render outputs and respond to inputs with R
server <- function(input, output, session) {
  output$hist <- renderPlot({
    hist(rnorm(input$n))
  })
}
# Wrap code in render*() functions before saving to output
# Refer to UI inputs with input$<id> and outputs with output$<id>
  
# Call shinyApp() to combine ui and server into an interactive app!
shinyApp(ui = ui, server = server)

See annotated examples of Shiny apps by running runExample(<example name>). Run runExample() with no arguments for a list of example names.

Share

Share your app in three ways:

1. Host it on shinyapps.io, a cloud based service from Posit. To deploy Shiny apps:

   • Create a free or professional account at shinyapps.io

   • Click the Publish icon in RStudio IDE, or run: rsconnect::deployApp("<path to directory>")

2. Purchase Posit Connect, a publishing platform for R and Python. posit.co/products/enterprise/connect/
3. Build your own Shiny Server. posit.co/products/open-source/shinyserver/

Outputs

render*() and *Output() functions work together to add R output to the UI.

Table of render*() functions and their associated *Output() functions.

render*() Functions	*Output() Functions
DT::renderDataTable(expr, options, searchDelay, callback, escape, env, quoted, outputArgs)	dataTableOutput(outputId)
renderImage(expr, env, quoted, deleteFile, outputArgs)	imageOutput(outputId, width, height, click, dblclick, hover, brush, inline)
renderPlot(expr, width, height, res, …, alt, env, quoted, execOnResixe, outputArgs	plotOutput(outputId, width, height, click, dblclick, hover, brush, inline)
renderPrint(expr, env, quoted, width, outputArgs)	verbatimTextOutput(outputId, placeholder)
renderTable(expr, striped, hover, bordered, spacing, width, align, rownames, colnames, digits, na, …, env, quoted, outputArgs)	tableOutput(outputId)
renderText(expr, env, quoted, outputArgs, sep)	textOutput(outputId, container, inline)
renderUI(expr, env, quoted, outputArgs)	uiOutput(outputId, inline, container, …) htmlOutput(outputId, inline, container, …)

These are the core output types. See htmlwidgets.org for many more options.

Inputs

Collect values from the user.

Access the current value of an input object with input$<inputId>. Input values are reactive.

• actionButton(inputId, label, icon, width, ...)

• actionLink(inputId, label, icon, ...)

• checkboxGroupInput(inputId, label, choices, selected, inline, width, choiceNames, choiceValues)

• checkboxInput(inputId, label, value, width)

• dateInput(inputId, label, value, min, max, format, startview, weekstart, language, width, autoclose, datesdisabled, daysofweekdisabled)

• dateRangeInput(inputId, label, start, end, min, max, format, startview, weekstart, language, separator, width, autoclose)

• fileInput(inputId, label, multiple, accept, width, buttonLabel, placeholder)

• numericInput(inputId, label, value, min, max, step, width)

• passwordInput(inputId, label, value, width, placeholder)

• radioButtons(inputId, label, choices, selected, inline, width, choiceNames, choiceValues)

• selectInput(inputId, label, choices, selected, multiple, selectize, width, size): Also selectizeInput()

• sliderInput(inputId, label, min, max, value, step, round, format, locale, ticks, animate, width, sep, pre, post, timeFormat, timezone, dragRange)

• textInput(inputId, label, value, width, placeholder): Also textAreaInput()

Reactivity

Reactive values work together with reactive functions. Call a reactive value from within the arguments of one of these functions to avoid the error Operation not allowed without an active reactive context.

Expand to read about the reactivity diagram

Phases in the reactivity diagram

• Create your own reactive values
  • reactiveValues()
  • reactiveFileReader()
  • reactivePoll()
  • *Input()
• Perform side effects
  • observeEvent()
  • observe()
• Schedule updates
  • invalidateLater()
• Create reactive expressions
  • reactive()
• Remove reactivity
  • isolate()
• React based on event
  • eventReactive()
• Render reactive output
  • render*()

Create Your own Reactive Values

• *Input() functions: Each input function creates a reactive value stored as input$<inputId>.

  # *Input() example
  ui <- fluidPage(
    textInput("a","","A")
  )

• reactiveVal(): Creates a single reactive values object.

  reactiveValues(...): Creates a list of reactive values whose values you can set.

  # reactiveVal example
  server <- function(input,output){
    rv <- reactiveValues() 
    rv$number <- 5
  }

Create Reactive Expressions

• reactive(x, env, quoted, label, domain):

  • Reactive expressions:

    • cache their value to reduce computation

    • can be called elsewhere

    • notify dependencies when invalidated

  Call the expression with function syntax, e.g. re().

  library(shiny)
  
  ui <- fluidPage(
    textInput("a","","A"), 
    textInput("z","","Z"), 
    textOutput("b")
    )
  
  server <- function(input,output){
    re <- reactive({ 
      paste(input$a,input$z)
    })
    output$b <- renderText({
      re()
    }) 
  }
  
  shinyApp(ui, server)

React Based on Event

• eventReactive(eventExpr, valueExpr, event.env, event.quoted, value.env, value.quoted, ..., label, domain, ignoreNULL, ignoreInit): Creates reactive expression with code in 2nd argument that only invalidates when reactive values in 1st argument change.

  library(shiny)
  
  ui <- fluidPage(
    textInput("a","","A"), 
    actionButton("go","Go"), 
    textOutput("b")
  )
  
  server <- function(input,output){
    re <- eventReactive(
      input$go,{input$a}
    )
    output$b <- renderText({
      re()
    }) 
  }

Render Reactive Output

• render*() functions: (see front page) Builds an object to display. Will rerun code in body to rebuild the object whenever a reactive value in the code changes. Save the results to output$<outputId>.

  library(shiny)
  
  ui <- fluidPage(
    textInput("a","","A"), 
    textOutput("b")
  )
  
  server <- function(input,output){
    output$b <-
      renderText({
        input$a
    })
  }
  
  shinyApp(ui, server)

Perform Side Effects

• observe(x, env): Creates an observer from the given expression.

• observeEvent(eventExpr, handlerExpr, event.env, event.quoted, handler.env, handler.quoted, ..., label, suspended, priority, domain, autoDestroy, ignoreNULL, ignoreInit, once): Runs code in 2nd argument when reactive values in 1st argument change. Alternative to observe``().

  library(shiny)
  
  ui <- fluidPage(textInput("a","","A"), actionButton("go","Go"))
  
  server <- function(input,output){
    observeEvent(input$go, {
      print(input$a)
    })
  }
  
  shinyApp(ui, server)

Remove Reactivity

• isolate(expr): Runs a code block. Returns a non-reactive copy of the results.

  library(shiny)
  
  ui <- fluidPage(
    textInput("a","","A"), 
    textOutput("b")
  )
  
  server <- function(input,output){ 
    output$b <- 
      renderText({
        isolate({input$a})
      })
  }
  
  shinyApp(ui, server)

UI

An app’s UI is an HTML document.

Use Shiny’s functions to assemble this HTML with R.

fluidPage(
  textInput("a","")
)

Returns HTML:

<div class="container-fluid">
  <div class="form-group shiny-input-container">
    <label for="a"></label>
    <input id="a" type="text" class="form-control" value=""/>
  </div>
</div>

Add static HTML elements with tags, a list of functions that parallel common HTML tags, e.g. tags$a(). Unnamed arguments will be passed into the tag; named arguments will become tag attributes.

Run names(tags) for a complete list. tags$h1("Header") -> <h1>Header</h1>

The most common tags have wrapper functions. You do not need to prefix their names with tags$.

ui <- fluidPage(
  h1("Header 1"), # <h1>Header 1</h1>
  hr(), # <hr>
  br(), # <br>
  p(strong("bold")), # <p><strong>bold</strong></p>
  p(em("italic")), # <p><em>italic</em></p>
  p(code("code")), # <p><code>code</code></p>
  a(href="", "link"), # <a href="">link</a>
  HTML("<p>Raw html</p>") # display raw html
)

To include a CSS file, use includeCSS(), or

1. Place the file in the www subdirectory

2. Link to it with:

   tags$head(
     tags$link(
       rel = "stylesheet", 
       type = "text/css", 
       href = "<file name>"
       )
     )

To include JavaScript, use includeScript(), or

1. Place the file in the www subdirectory

2. Link to it with:

   tags$head(tags$script(src = "<file name>"))

To include an image:

1. Place the file in the www subdirectory

2. Link to it with:

   img(src = "<file name>")

Layouts

Use the bslib package to lay out the your app and its components.

Page layouts

Dashboard layouts

• page_sidebar() - A sidebar page

• page_navbar() - Multi-page app with a top navigation bar

• page_fillable() - A screen-filling page layout

Basic layouts

• page()

• page_fluid()

• page_fixed()

User interface layouts

Multiple columns

• layout_columns() - Organize UI elements into Bootstrap’s 12-column CSS grid

• layout_column_wrap() - Organize elements into a grid of equal-width columns

Multiple panels

• navset_tab() - Tabbed navigation container

• navset_pill() - Creates a navigation container that behaves exactly like navset_tab(), but the tab toggles are pills or button-shaped

• navset_underline() - Creates a navigation container that behaves exactly like navset_tab() and navset_pill(), but the active/focused navigation links are styled with an underline

• nav_panel() - Content to display when given item is selected

• nav_menu() - Create a menu of nav items

• nav_item() - Place arbitrary content in the nav panel

• nav_spacer() - Add spacing between nav items

Also dynamically update nav containers with nav_select(), nav_insert(), nav_remove(), nav_show(), nav_hide().

Sidebar layout

• sidebar()

• layout_sidebar()

• toggle_sidebar()

Themes

Use the bslib package to add existing themes to your Shiny app ui, or make your own.

library(bslib)
ui <- fluidPage(
  theme = bs_theme(
    boothswatch = "darkly",
    ...
  )
)

• bootswatch_themes(): Get a list of themes.

Build your own theme by customizing individual arguments.

bs_theme(
  bg = "#558AC5",
  fg = "#F9B02D",
  ...
)

• ?bs_theme for a full list of arguments.

• bs_themer(): Place within the server function ot use the interactive theming widget.

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CC BY SA Posit Software, PBC • info@posit.co • posit.co

Learn more at shiny.rstudio.com

Updated: 2024-05.

packageVersion("shiny")

[1] '1.8.1.1'

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