Stop reactions with isolate()

Ordinarily, the simple act of reading a reactive value is sufficient to set up a relationship, where a change to the reactive value will cause the calling expression to re-execute. The isolate() function allows an expression to read a reactive value without triggering re-execution when its value changes.

In this exercise, you will use the isolate() function to stop reactive flow.

Questo esercizio fa parte del corso

Building Web Applications with Shiny in R

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Istruzioni dell'esercizio

Update the server code so that the text output updates only when user changes the height or weight, and NOT the name.

esercizio interattivo pratico

Prova questo esercizio completando questo codice di esempio.

ui <- fluidPage(
  titlePanel('BMI Calculator'),
  sidebarLayout(
    sidebarPanel(
      textInput('name', 'Enter your name'),
      numericInput('height', 'Enter your height (in m)', 1.5, 1, 2, step = 0.1),
      numericInput('weight', 'Enter your weight (in Kg)', 60, 45, 120)
    ),
    mainPanel(
      textOutput("bmi")
    )
  )
)

server <- function(input, output, session) {
  rval_bmi <- reactive({
    input$weight/(input$height^2)
  })
  output$bmi <- renderText({
    bmi <- rval_bmi()
    # MODIFY CODE BELOW: 
    # Use isolate to stop output from updating when name changes.
    paste("Hi", input$name, ". Your BMI is", round(bmi, 1))
  })
}

shinyApp(ui = ui, server = server)

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