Shiny Package in R Programming

The package is an appropriate way to organize the work and share it with others. Packages in the R language are a collection of R functions, compiled code, and sample data. They are stored under a directory called “library” in the R environment. By default, R installs a set of packages during installation. One of the most important packages in R is the Shiny package. Shiny is an R package that makes it easy to build interactive web apps straight from R. It helps to host standalone apps on a webpage or embed them in R Markdown documents or build dashboards. One can also extend Shiny apps with CSS themes, htmlwidgets, and JavaScript actions.

Installation 

To use a package in R programming one must have to install the package first. This task can be done using the command install.packages(“packagename”). To install the whole Shiny package type this:

install.packages("shiny")


Shiny_installation

To install the latest development builds directly from GitHub, run this instead:

if (!require("remotes"))
  install.packages("remotes")
remotes::install_github("rstudio/shiny")


Important Verb Functions in Shiny Package

  • fluidPage(): It creates a page with a fluid layout. A fluid page layout consists of rows which in turn include columns. Rows exist for the purpose of making sure their elements appear on the same line and columns exist for the purpose of defining how much horizontal space within a 12-unit wide grid. Fluid pages scale their components in real-time to fill all available browser width.

   Syntax:



   fluidPage(…, title = NULL, theme = NULL)

Parameter

Description

Elements to include within the page.
title The browser window title.
theme Alternative Bootstrap stylesheet.

Example:

This is a basic shiny app template. 

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# import shiny package
library(shiny)
  
# define a page with fluid layout
ui <- fluidPage(h1("GeeksforGeeks article on shiny package in R"),
                p(style = "font-family:Impact", "My first shiny app")
)
server <- function(input, output) {}
  
shinyApp(ui = ui, server = server)

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Output:

FluidPage

  • shinyApp(): It creates Shiny app objects from either an explicit UI/server pair or bypassing the path of a directory that contains a Shiny app.

   Syntax:



   shinyApp(ui, server, onStart = NULL, options = list(), uiPattern = “/”, enableBookmarking = NULL)

   shinyAppDir(appDir, options = list())

   shinyAppFile(appFile, options = list())</p 
 

Parameter

Description

ui The UI definition of the app.
server

It has three parameters: input, output, and session.

It is called once for each session to ensure that each app is independent.

onStart A function that will be called before the app is actually run.
options Options that should be passed to the runApp.
uipattern

A regular expression that will be applied to each 

GET request to determine whether the ui should be used to handle the request.

enableBookmarking Can be “url”, “server”, or “disable”.The default value is NULL.
appDir Path to directory that contains a Shiny app.
appFile Path to a .R file containing a Shiny application.

Example:

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# import shiny package
library(shiny)
  
# define fluid page layout
ui <- fluidPage(
  sliderInput(inputId = "num"
              label = "Choose a number"
              value = 10, min = 1, max = 1000),
  plotOutput("hist")
)
  
server <- function(input, output)
{
  output$hist <- renderPlot({
    hist(rnorm(input$num))
  })
}
  
# create shiny app object 
# using shinyApp
shinyApp(ui = ui, server = server)

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Output:

shinyApp

  • reactive(): It creates a reactive expression. A reactive expression is an expression whose result will change over time.reactive() wraps a normal expression to create a reactive expression.

   Syntax:

   reactive(x, env = parent.frame(), quoted = FALSE, label = NULL)

Parameter

Description

x An expression.
env The parent environment for reactive expression.
quoted

Is the expression quoted? By default, this is FALSE. 

This is useful when you want to use an expression that is stored in a variable

label A label for reactive expression.

Example:

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# import shiny package
library(shiny)
  
# define fluid page layout
ui <- fluidPage(
  textInput(inputId = "num", label = "Choose a number"
            value = "", width = 100, placeholder = NULL),
  plotOutput("hist"),
  verbatimTextOutput("stats")
)
server <- function(input, output) 
{
  # use reactive to create
  # a reactive expression
  data <- reactive({rnorm(input$num)})
    
  output$hist <- renderPlot({hist(data())})
  output$stats <- renderPrint({summary(data())})
}
  
# create shiny app object 
# using shinyApp
shinyApp(ui = ui, server = server)

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Output:



reactive_50

Now, change the input value from 50 to 100 to see what happens.

reactive_100

The output values(histogram and summary) also change with the alternation in the input values, i.e the app has reactivity.

  • observeEvent(): It triggers code to run on servers. Respond to “event-like” reactive inputs, values, and expressions.

Syntax:

observeEvent(eventExpr, handlerExpr, event.env = parent.frame(), event.quoted = FALSE, handler.env = parent.frame(), handler.quoted = FALSE, label = NULL, suspended = FALSE, priority = 0, domain = getDefaultReactiveDomain(), autoDestroy = TRUE, ignoreNULL = TRUE, ignoreInit = FALSE, once = FALSE)

Parameter

Description

eventExpr

A expression that represents the event.It can be

 a simple or a complex reactive expression.

handler.Expr The expression to call whenever eventExpr is invalidated.
event.env

The parent environment for eventExpr. 



By default, this is the calling environment.

event.quoted

Returns whether the eventExpr expression is quoted or not.

 By default, this is FALSE.

handler.env The parent environment for handlerExpr. By default, this is the calling environment.
handler.quoted

Returns whether the handlerExpr expression is quoted or not.

 By default, this is FALSE.

label A label for the observer or reactive
suspended If TRUE, start the observer in a suspended state.
priority

An integer or numeric that controls the priority 

with which this observer should be executed.Positive,Negative and Zero values are allowed.

autodestroy

If TRUE (the default), the observer will be automatically 

destroyed when its domain (if any) ends.

ignoreNULL Whether the action should be triggered when the input is NULL.
ignoreInit

If TRUE, then, when this observeEvent is first created/initialized,



ignore the handlerExpr (the second argument), whether

 it is otherwise supposed to run or not. The default is FALSE.

once

Whether this observeEvent should be immediately destroyed after

 the first time that the code in handlerExpr is run.

Example:

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# import shiny package
library(shiny)
  
# define fluid page layout
ui = fluidPage(
  textInput(inputId = "num"
            label = "Enter a numeric value", value = "10"),
            actionButton("button", "Calculate"),
  column(8, tableOutput("table"))
)
  
server = function(input, output)
{
  # Take an action every time button is pressed
  observeEvent(input$button, {
    cat("Showing", input$num, "rows\n")
  })
    
  # Take a reactive dependency 
  # on input$num, but not on any 
  # of the stuff inside the function
  df <- eventReactive(input$button, {
    head(cars, input$num)
  })
  output$table <- renderTable({
    df()
  })
}
  
# create shiny app object 
# using shinyApp
shinyApp(ui, server)

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Output:

observeEventobserveEvent

  • eventReactive(): A reactive expression that only responds to specific values. Respond to “event-like” reactive inputs, values, and expressions.

Syntax:

eventReactive(eventExpr, 
valueExpr, 
event.env = parent.frame(), 
event.quoted = FALSE, 
value.env = parent.frame(), 
value.quoted = FALSE, 
label = NULL, 
domain = getDefaultReactiveDomain(), 
ignoreNULL = TRUE, 
ignoreInit = FALSE)



Parameter

Description

eventExpr A expression that represents the event.It can be a simple or a complex reactive expression.
valueExpr It produces the return value of the eventReactive. It will be executed within an isolate() scope.
event.env The parent environment for eventExpr. By default, this is the calling environment.
event.quoted Returns whether the eventExpr expression is quoted or not. By default, this is FALSE.
value.env The parent environment for valueExpr. By default, this is the calling environment.
value.quoted Returns whether the valueExpr expression is quoted or not. By default, this is FALSE.
ignoreNULL Whether the action should be triggered when the input is NULL.
ignoreInit

If TRUE, then, when this observeEvent is first created/initialized,

 ignore the handlerExpr (the second argument), whether

 it is otherwise supposed to run or not. The default is FALSE.

Example:

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# import shiny package
library(shiny)
  
# define fluid page layout
ui <- fluidPage(
  sliderInput(inputId = "num"
              label = "Choose a number"
              value = 25, min = 1, max = 100),
  actionButton(inputId = "go"
               label = "Update"),
  plotOutput("hist")
)
  
server <- function(input, output)
{
  data <- eventReactive(input$go, {
    rnorm(input$num) 
  })
    
  output$hist <- renderPlot({
    hist(data())
  })
}
  
# create shiny app object 
# using shinyApp
shinyApp(ui = ui, server = server)

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Output:

eventReactive

Here, the output does not change with the input values until and unless the update button is triggered

eventReactive



  • actionButton(): It creates an action button or a link. Their initial value is zero, and increments by one each time it is pressed.

   Syntax:

   actionButton(inputId, label, icon = NULL, width = NULL, …)

   actionLink(inputId, label, icon = NULL, …)

Parameter

Description

inputId The input slot that will be used to access the value.
label The contents of the button or link.
icon An optional icon() to appear on the button.
width The width of the input(ex-‘200px’,or’100%’).
…. Named attributes to be applied to the button or link.

Example:

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# import shiny package
library(shiny)
  
# define fluid page layout
ui <- fluidPage(
  sliderInput("obs", "Number of observations", 0, 1000, 500),
  actionButton("goButton", "Go!", class = "btn-success"),
  plotOutput("distPlot")
)
  
server <- function(input, output)
{
  output$distPlot <- renderPlot({
    input$goButton
    dist <- isolate(rnorm(input$obs))
    hist(dist)
  })
}
  
# create shiny app object 
# using shinyApp
shinyApp(ui, server)

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Output:

actionButton

The output gets updated as soon as the actionButton(Go!) is clicked.

actionButton



  • checkboxGroupInput(): It creates a group of checkboxes that can be used to toggle multiple choices independently. The server will receive the input as a character vector of the selected values.

Syntax:

checkboxGroupInput(inputId, label, choices = NULL, selected = NULL, inline = FALSE, width = NULL, choiceNames = NULL, choiceValues = NULL)

Parameter

Description

inputId The input slot that will be used to access the value.
label The contents of the button or link.
choices

List of values to show checkboxes for. If elements of 

the list are named then that name rather than the value is displayed to the user.

selected The initial selection.
inline If TRUE, render the choices horizontally.
width The width of the input(ex-‘200px’,or’100%’).
choiceValues, choiceNames List of names and values.

Example:

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# import shiny package
library(shiny)
  
# define fluid page layout
ui <- fluidPage(
  checkboxGroupInput("icons", "Choose icons:",
                     choiceNames =
                       list(icon("dog"), icon("cat"),
                            icon("fish"), icon("bug")),
                     choiceValues =
                       list("dog", "cat", "fish", "bug")),
                     textOutput("txt")
)
  
server <- function(input, output, session) 
{
  output$txt <- renderText({
    icons <- paste(input$icons, collapse = ", ")
    paste("You chose", icons)
  })
}
  
# create shiny app object 
# using shinyApp
shinyApp(ui = ui, server = server)

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Output:

checkboxGroupInput



  • textInput(): It creates a text input label.

   Syntax:

   textInput(inputId, label, value = “”, width = NULL, placeholder = NULL)

Parameter

Description

inputId The input slot that will be used to access the value.
label The contents of the button or link.
value The initial value.
width The width of the input(ex-‘200px’,or’100%’).
placeholder A character string giving the user a hint as to what can be entered into the control.

Example:

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# import shiny package
library(shiny)
  
# define fluid page layout
ui <- fluidPage(
  textInput("txt", "Enter yoour text here", "Empty"),
  verbatimTextOutput("value")
)
  
server <- function(input, output)
{
  output$value <- renderText({ input$text })
}
  
# create shiny app object 
# using shinyApp
shinyApp(ui, server)

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Output

textInput

  • textOutput(): It creates a text output element. Render a reactive output variable as text within an application page.

   Syntax:

   textOutput(outputId, container = if (inline) span else div, inline = FALSE)

Parameter

Description



outputId The output variable to read the value from.
container A function to generate an HTML element to contain the text.
inline Use an inline (span()) or block container (div()) for the output.

Example:

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# import shiny package
library(shiny)
  
# define fluid page layout
ui <- fluidPage(
 textInput(inputId = "Name", label = "Enter your name"),
 textOutput("txt")
)
  
server <- function(input, output, session) 
{
  output$txt <- renderText({
    Name <- paste(input$Name, collapse = ", ")
    paste("Welcome! to geeksforgeeks ", Name)
  })
}
  
# create shiny app object 
# using shinyApp
shinyApp(ui = ui, server = server)

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Output:

textOutput

  • wellPanel(): Creates a panel with a slightly inset border and gray background.

   Syntax:

   wellPanel(…)

Parameter

Description

UI elements to include inside the panel.

Example:

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# import shiny package 
library(shiny)
  
# define fluid page layout
ui <- fluidPage(
    sliderInput(inputId = "num"
                label = "Choose a number"
                value = 25, min = 1, max = 100),
    
 # define plot inside
 # a wellPanel 
 wellPanel(plotOutput("hist"))
)
  
server <- function(input, output)
{
  output$hist <- renderPlot({
    hist(rnorm(input$num), main = input$title)
  })
}
  
# create shiny app object 
# using shinyApp
shinyApp(ui = ui, server = server)

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Output:

wellPanel

Observe that the histogram lies inside a gray-colored box(wellPanel).




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