R Shiny

Vahid Mirjalili, Data Scientist

We want to create a data application to be posted on a company's website, where users can play interactively with the app, for example change the bin of histograms, ... then shiny, a framework for creating interactive web applications, is the right tool for this.

Shiny tutorial is a good resource for learning: tutorial

A shiny project must have at least two parts:

a user interface script (ui.R): controls layout and appearance of the app
a server script (server.R): does the computations behind the scene

Example of ui.R:



In [1]:

    
## ui.R
library(shiny)
shinyUI(pageWithSidebar(
    ## Header 
    headerPanel("Hello Shiny World!"),

    sidebarPanel(
        h3('This is a sidebar created')
    ),

    mainPanel(
        h3('This is the main panel')
    )
))



In [2]:

    
## server.R
library(shiny)
shinyServer(
    function(input, output) {
        ##  ## 
    }
)

To run this application, change the working directory to the app directory and use runApp()

The result will be displayed in the browser as below:



In [ ]:

    
setwd("R-shiny/app-01")
getwd()
list.files()
runApp()

# or use the directory address:

runApp("/home/vahid/GitHub/DataScience/R-shiny/")

Shiny Gallery provides a lot of nice example, that you can change for your application.

Or you can run pre-built examples in the shiny package:



In [ ]:

    
system.file("examples", package="shiny")

runExample("05_sliders")   ## -> interactive slider bars
runExample("06_tabsets")   ## -> multiple panels through menu-bar
runExample("10_download")  ## -> a wizard to download files
runExample("11_timer")     ## -> displays running date and time









    Out[ ]:





[1] "/home/vahid/R/x86_64-pc-linux-gnu-library/3.1/shiny/examples"






    



simpleMessage in message("\n", "Listening on http://", host, ":", port): 
Listening on http://127.0.0.1:4238

Options:

layout:

fluidPage automatically adjusts to the browser dimension
sidebarLayout to add a sidebar, that needs two arguments
- sidebarPanel()
- mainPanel()
- optional argument position=.. where default is "left"
HTML tags can be used directly in ui.R, firexampl p() for < p >, h1() for header < h1 >, img() for < img >

To Get User Input:

numericInput()
- arguments: inputId, label, value, min=NA, max=NA, step=NA
checkboxGroupInput()
- arguments: inputId, label, choices, selected=Null
- choices is a vector: c("value 0" = "0", "value 1" = "1", "value 2" = "2")

dateInput()
- arguments: inputId, label, value = NULL, min=NULL, max = NULL, format = "yyyy-mm-dd", ..
submitButton()
- argument: test to display

To Print Output:

verbatimText()
- argument: outputId



In [ ]:

    
## ui.R
## example for user input and output:

library(shiny)

shinyUI(fluidPage(
    titlePanel("Input/output functionality in Shiny!"),

    sidebarLayout( position="left",
        numericInput("id1", "Number of Random Points", 40, min=10, max=100, step=5),
        checkboxGroupInput("id2", "Number of Dimensions:", c("v1"="1", "v2"="2", "v3"="3"))
    ),

    mainPanel(
        h2('Output: '),
        h3('Distance between class means:'),
        verbatimTextOutput("oid1")
    )
))



In [ ]:

    
## server.R 
## example for user input and output:

library(shiny)

shinyServer(
    function(input, output) {
        n  <- input$id1 ## number of random points
        w1 <- rnorm(n, mean=0, sd=1)
        w2 <- rnorm(n, mean=1, sd=2)
        m1 <- mean(w1)
        m2 <- mean(w2)
        output$oid1 <- renderPrint({m1 - m2})
    }
)

Reactive Expression

Reactive expressoin are those which only need to be updated when their input is changed. A reactive expression is made by reactive({}) expression:

Example:

my.react.xpr <- reactive({d <- rnorm(input$id1); mean(d)})

Call a reactive expression like calling a function; example: my.react.xpr()
Only call reactive expressions inside other reactive expressions or inside render* functions