Shiny

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What is Shiny?

• R package

• Web application framework for R

• interactive web page

• interactivity with R

• Great for sharing R program with someone not knowing R

Two parts

• a web page that shows the app to the user

• a computer that powers the app

• your own computer

• a server

Shiny Template

library(shiny)

#User Interface ui <- fluidpage()

#Server code (R)

server <- function(input,output){}

shinyApp(ui = ui, server = server) Very Important

• name of the file app.R

• in its own folder

Alternate Method

• useful when the app is complex and involves lots of code

Two Files in the same folder

• UI: ui.R

• Server: server.R

Layout

ui <- fluidPage(

titlePanel("title panel"),

sidebarLayout(# always two arguments sidebarPanel("sidebar panel"), mainPanel("main panel")

) )

Layout

ui <- fluidPage(

titlePanel("title panel"),

sidebarLayout(

position = "right",# change sidebar position sidebarPanel("sidebar panel"),

mainPanel("main panel") )

)

Text in Panel

mainPanel(

h1("Big Title"),

p("p creates a paragraph of text."), h3("Third level title"),

code("text similar to computer code") )

All UI functions are simply HTML wrappers

ui <- fluidPage(

titlePanel("title panel"), sidebarLayout(

sidebarPanel("sidebar panel"), mainPanel("main panel")

) )

print(ui)

## <div class="container-fluid">

## <h2>title panel</h2>

## <div class="row">

## <div class="col-sm-4">

## <form class="well">sidebar panel</form>

## </div>

## <div class="col-sm-8">main panel</div>

## </div>

## </div>

Reactivity

For reactivity, app needs inputs and outputs Steps

• Add input to the UI

• Add an R object (output) to the UI

• Tell Shiny how to build the object in the server function

Reactivity

The object will be reactive if the code that builds it calls a widget value.

Add inputs to the UI

Example with iris

sidebarPanel(

selectInput("var", # name to access the widget’s value label = "Choose a variable to display", choices = list("Sepal Length",

"Sepal Width",

"Petal Length",

"Petal Width"), selected = "Sepal Length") )

More widgets

List of function

• actionButton: action Button

• checkboxGroupInput: group of check boxes

• checkboxInput: single check box

• dateInput: calendar to aid date selection

• dateRangeInput: pair of calendars for selecting a date range

• fileInput: file upload control wizard

• helpText: help text that can be added to an input form

• numericInput: field to enter numbers

• radioButtons: set of radio buttons

• selectInput: box with choices to select from

• sliderInput: slider bar

• submitButton: submit button

• textInput: field to enter text Link to Widget Gallery

Add an R object (output) to the UI

mainPanel(

textOutput("selected_var") )

List of Output functions

• dataTableOutput: DataTable

• tableOutput: table

• plotOutput: plot

• htmlOutput: raw HTML

• imageOutput: image

• textOutput: text

• uiOutput: raw HTML

• verbatimTextOutput: text

Provide R code to build the object

server <- function(input, output) { output$selected_var <- renderText({

paste("You have selected", input$var) })

}

Provide R code to build the object

server <- function(input, output) { output$selected_var <- renderText({

paste("You have selected", input$var) })

}

List of Render functions

• renderDataTable: DataTable

• renderImage: images (saved as a link to a source file)

• renderPlot: plots

• renderPrint: any printed output

• renderTable: data frame, matrix, other table like structures

• renderText: character strings

• renderUI: a Shiny tag object or HTML

Add a Plot - UI

ui <- fluidPage(

titlePanel("Final App"), sidebarLayout(

sidebarPanel(

selectInput("var",

label = "Choose a variable to display", choices = list("Sepal Length",

"Sepal Width",

"Petal Length",

"Petal Width"), selected = "Sepal Length") ),

mainPanel(

textOutput("selected_var"), plotOutput("plot_output") )

) )

Add a Plot - Server

server <- function(input, output) { output$selected_var <- renderText({

paste("Distribution of", input$var, "by Species") })

output$plot_output <- renderPlot({

variable<- switch(input$var,

"Sepal Length" = iris$Sepal.Length,

"Sepal Width" = iris$Sepal.Width,

"Petal Length" = iris$Petal.Length,

"Petal Width" = iris$Petal.Width )

data<-data.frame(variable=variable, Species=iris$Species) boxplot(data$variable~data$Species,las=1) })

}

switch: useful companion to multiple choice Shiny widgets

Result with a Plot - App

Summary

In the UI

• *Inputfunction: create input

• *Output function: place reactive objects in your Shiny app In the server

• render* function: tell Shiny how to build the objects

• surround R expressions by curly braces, {}, in eachrender*

function

• save yourrender\*expressions in the output list, with one entry for each reactive object in your app, and

• create reactivity by including an input value in arender\*

expression

Don’t forget

• The directory that app.R appears in will become the working directory of the Shiny app

• Shiny will run code placed at the start of app.R, before the server function, only once during the life of the app.

• Shiny will run code placed inside server function multiple times, which can slow down the app.

• use of reactive function

Reactivity

• input$var is a reactive value

• output$selected_var depends on input$var

• if input$varchanges, thenoutput$selected_varreacts

• All inputs are automatically reactive, so if you use any input inside arender* function, the output will re-render any time input changes

Reactive contexts

• You can define your own reactive variables

• Reactive values can only be used inside reactive contexts

• Any render*function is a reactive context

• Usereactive({...}) to assign a reactive variable

• Useobserve({...}) to access a reactive variable Remember

• reactive variable means anything that depends on it gets re-executed automatically

Reactive contexts - Assign a variable

#WRONG

server <- function(input, output) { x <- input$num + 1

}

#Right

server <- function(input, output) { x <- reactive({

input$num + 1 }) }

Reactive contexts - See a variable

#WRONG

server <- function(input, output) { print(input$num)

}

server <- function(input, output) { observe({

print(input$num) })

}

Sharing Shiny Apps

• as R script

• simplest

• works only if the users have R on their own computer

• as a web page

• more user friendly

• users only need web browser

• how

• host the app yourself (see with your IT departement)

• use RStudio support: Shinyapps.io, Shiny Server (Pro)

Around Shiny

• Shiny in RMarkdown document Header

---

title: "Shiny Document"

output: html_document runtime: shiny

---

in chunk

numericInput("rows", "How many cars?", 5) renderTable({

head(cars, input$rows) })

• ShinyDashboard

More complex App