Slow and steady wins the race - eventReactive()

Ottavia M. Epifania

eventReactive() and actionButton()

These functions are usually employed together:

The action button

actionButton("start", 
             "Press here to do something")

The action button controlling the actions

ui = fluidPage(
  [...]
  actionButton("start",
             "Press here to do something")
)
server = server(input, output) {
  data = eventReactive(input$start,
                    [...]
                       )
}

1

Define the button label to be used in the server

2

Define the action after which the button event becomes reactive

3

Code and operations to be performed after the button has been pressed

An example

Choose a dataset:

rock pressure cars

• UI
• Server
• Together

ui <- fluidPage(
    sidebarLayout(sidebarPanel(
        selectInput(inputId = "dataset",
                    label = "Choose a dataset:",
                    choices = list("rock" = 1, 
                                   "pressure" = 2,
                                   "cars" = 3)), 
      actionButton("load", "Select dataset")
      ),
mainPanel(
      plotOutput(
          "graph"   
        ), 
      verbatimTextOutput( 
          "summary"   
      ))))

1

Action button visible in the UI

server <- function(input, output){
    dataInput <- eventReactive(input$load, {
      if(input$dataset == 1){
        data <- rock
      } else if (input$dataset == 2 ){
        data <- pressure
      } else if (input$dataset == 3) {
        data <- cars
      }
    }
    )
output$graph <- renderPlot({
      data <- dataInput()
      plot(data[, c(1:2)])
    })
output$summary <- renderPrint({
      data <- dataInput()
      summary(data[, c(1:2)])
    })
  }

1

Use eventReactive to make the app “react” after a specific action (e.g., clicking on the action button)

2

Normal code, in this case defining the specific dataset

3

Actually makes the dataset usable for the analysis

shinyApp(ui, server)