Non-reactive scope in Shiny

Question

In my Shiny App, there are two inputs: the number of observations (an integer), and the color (a character to be choosen between red, green and blue). There is also a "GO!" action button.

Which Shiny function to use in order to:

have the random numbers regenerated and the histogram updated with this new data only when the user click on the "Go!" button.
be able to change the color of the histogram on the fly without regenerating the random numbers.

I would prefer a solution that provides the maximum clarity to the code.

See below one of my unsuccessful tentative with isolate.

# DO NOT WORK AS EXPECTED

# Define the UI
ui <- fluidPage(
  sliderInput("obs", "Number of observations", 0, 1000, 500),
  selectInput('color', 'Histogram color', c('red', 'blue', 'green')),
  actionButton("goButton", "Go!"),
  plotOutput("distPlot")
)

# Code for the server
server <- function(input, output) {
  output$distPlot <- renderPlot({
    # Take a dependency on input$goButton
    input$goButton

    # Use isolate() to avoid dependency on input$obs
    data <- isolate(rnorm(input$obs))
    return(hist(data, col=input$color))
  })
}

# launch the App
library(shiny)
shinyApp(ui, server)

Pork Chop Pork Chop · Accepted Answer · 2017-03-15T11:32:38

Something like this? It will only update the data() variable upon button click. You can read up on the observeEvent and eventReactive here

#rm(list = ls())
# launch the App
library(shiny)
ui <- fluidPage(
  sliderInput("obs", "Number of observations", 0, 1000, 500),
  selectInput('color', 'Histogram color', c('red', 'blue', 'green')),
  actionButton("goButton", "Go!"),
  plotOutput("distPlot")
)

# Code for the server
server <- function(input, output) {
  data <- eventReactive(input$goButton,{
    rnorm(input$obs)
  })
  
  output$distPlot <- renderPlot({
    return(hist(data(), col=input$color))
  })
}
shinyApp(ui, server)

Non-reactive scope in Shiny

1 Answers