Shiny for Interactive Application Development using R

Vivek Patil
Associate Professor of Marketing, Gonzaga University

What is shiny

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

Components of an application

Two files

  1. User-Interface file (ui.R) - inputs and display of output in a customizable layout
  2. Server (server.R) - the work-horse that takes inputs, processes them, and creates outputs to display in the user-interface

Developing a sample application using iris

Sepal length and width and Petal length and width of 50 flowers from each of 3 species of iris - setosa, versicolor, and virginica

  1. View data (or a part of it)
  2. Summarize data
  3. 2 graphs of data - a scatter plot and a box plot

View Data

head(iris,5)

##   Sepal.Length Sepal.Width Petal.Length Petal.Width Species
## 1          5.1         3.5          1.4         0.2  setosa
## 2          4.9         3.0          1.4         0.2  setosa
## 3          4.7         3.2          1.3         0.2  setosa
## 4          4.6         3.1          1.5         0.2  setosa
## 5          5.0         3.6          1.4         0.2  setosa

# tail(iris,n) 
# iris

Summarize Data

summary(iris)

##   Sepal.Length   Sepal.Width    Petal.Length   Petal.Width 
##  Min.   :4.30   Min.   :2.00   Min.   :1.00   Min.   :0.1  
##  1st Qu.:5.10   1st Qu.:2.80   1st Qu.:1.60   1st Qu.:0.3  
##  Median :5.80   Median :3.00   Median :4.35   Median :1.3  
##  Mean   :5.84   Mean   :3.06   Mean   :3.76   Mean   :1.2  
##  3rd Qu.:6.40   3rd Qu.:3.30   3rd Qu.:5.10   3rd Qu.:1.8  
##  Max.   :7.90   Max.   :4.40   Max.   :6.90   Max.   :2.5  
##        Species  
##  setosa    :50  
##  versicolor:50  
##  virginica :50  
##                 
##                 
##

Plot 1 - Scatter plot

library(ggplot2)
ggplot(iris,aes(x=Sepal.Length,y=Sepal.Width,color=Species))+geom_point()

plot of chunk unnamed-chunk-4

Plot 2 - Box plot

ggplot(iris,aes(x=Species,y=Sepal.Length))+geom_boxplot()

plot of chunk unnamed-chunk-5

Recap

  1. View data (or a section of it) (using head, tail, or just the entire data)
  2. Summarize data (using summary)
  3. 2 graphs of data - a scatter plot (x= Sepal.Length, y= Sepal.Width) and a box plot (how distribution of Sepal.Length varied across the three Species)

Imagine the difficulty below

  1. What if one wanted the ability to specify any variable for x and y axes of the scatter plot?
  2. What if one wanted to alter the variable whose distribution one wanted to plot across the three species in the box plot?
  3. What if one wanted to select a subset of the data (any range of any of the 4 numeric variables) and wanted to see how the data, summary, and the two plots changed?

Let's work on the user interface

Our Widgets

  • One "Select box" each for the x-variable and y-variable (for scatter plot), and one "Select box" for the dvariable (for distribution to study in box plot) - The options for each of the 4 select boxes will be the same, the four numeric variables
  • One "Slider range" for each of the four numeric variables - the minimum and maximum for each "Slider range" should be the minimum and maximum of the variable they are representing. Default state of each: The entire range (complete dataset)

Input widgets for user interface

# The 5th variable in the iris dataset is not numeric - Species - Not a choice option 
selectInput("xvar", "x-variable:", choices=names(iris[,-5]))
selectInput("yvar", "y-variable:", choices=names(iris[,-5]),selected = names(iris[2]))
selectInput("dvar", "Distribution of which variable for box plot?", choices=names(iris[,-5]), selected = names(iris[3]))

sliderInput("Sepal.Length", label = "Sepal.Length", min = min(iris$Sepal.Length), max = max(iris$Sepal.Length), 
            value=c(min(iris$Sepal.Length),max(iris$Sepal.Length)))

sliderInput("Sepal.Width", label = "Sepal.Width", min = min(iris$Sepal.Width), 
                       max = max(iris$Sepal.Width), value = c(min(iris$Sepal.Width),max(iris$Sepal.Width)))

sliderInput("Petal.Length", label = "Petal.Length", min = min(iris$Petal.Length), 
                       max = max(iris$Petal.Length), value = c(min(iris$Petal.Length),max(iris$Petal.Length)))

sliderInput("Petal.Width", label = "Petal.Width", min = min(iris$Petal.Width), 
                       max = max(iris$Petal.Width), value = c(min(iris$Petal.Width),max(iris$Petal.Width)))

Output spots in ui.r

Output Spots and their unique names in ui.R

dataTableOutput(outputId="subsetdata")

To present an interactive table of the entire data using the jQuery library DataTables

verbatimTextOutput("summary")

For a verbatim textOutput of the summary function

plotOutput("scatterplot")

plotOutput("boxplot")

For each of the two plots - the scatter plot and the box plot

Laying out the ui.R

The ui with no output

server.R

  • Take inputs from sliders and subset the data
    • Display resulting subset using datatable (name: "subsetdata" in ui.r)
  • Compute summary of subsetted data and ship it off to "summary" in ui.r
  • Take inputs for x and y variable
    • Create scatter plot using the ggplot2 package and ship this off to "scatterplot" in ui.r
  • Take input for dvar (for distribution variable) and create box plot
    • Create box plot using ggplot2 and ship this last piece off to "boxplot" in ui.r

Don't forget, the input variable names in the server should be the same ones the ui.r is sending to it.

Subsetting data

  • Creating dataset that is reactive to the inputs from the 4 sliders
  • Each of those sliders returns two values, the lower and upper bounds of the range
dataset=reactive(iris[(iris$Sepal.Length>=input$Sepal.Length[1] & iris$Sepal.Length<=input$Sepal.Length[2]&
                            iris$Sepal.Width>=input$Sepal.Width[1] & iris$Sepal.Width<=input$Sepal.Width[2]&
                               iris$Petal.Length>=input$Petal.Length[1] & iris$Petal.Length<=input$Petal.Length[2]&
                                  iris$Petal.Width>=input$Petal.Width[1] & iris$Petal.Width<=input$Petal.Width[2]),])

More information on "reactivity" can be found here: http://shiny.rstudio.com/articles/reactivity-overview.html

Rendering the outputs

Source: http://shiny.rstudio.com/tutorial/lesson4/

Render function Creates
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

Creating the outputs

output$subsetdata <- renderDataTable(dataset(),options=list(pageLength=10)) # for Data table

output$summary <- renderPrint(summary(dataset()))

output$scatterplot=renderPlot(ggplot(dataset(),aes_string(x=input$xvar, y=input$yvar,color="Species"))+ geom_point()+ggtitle("Scatter Plot"))

output$boxplot=renderPlot(ggplot(dataset(),aes_string(x="Species",y=input$dvar))+ geom_boxplot()+ ggtitle("Box Plot"))
  • Note how the reactive dataset is referred to as dataset()
  • Since the inputs from "Select box" show up as strings, we use aes_string instead of aes in our ggplot creations

Putting it all together with some instructions and messages

Deploying/Sharing an Application

Few Resources