Add another reactive expression

A reactive expression can call other reactive expressions. This allows you to modularize computations and ensure that they are NOT executed repeatedly. Mastering the use of reactive expressions is key to building performant Shiny applications.

In this exercise, you will use a reactive expression to calculate the health status based on the BMI.

Deze oefening maakt deel uit van de cursus

Building Web Applications with Shiny in R

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Oefeninstructies

Add a reactive expression rval_bmi_status to calculate BMI status.
Use this reactive expression to replace BMI status calculations in the output.

Praktische interactieve oefening

Probeer deze oefening eens door deze voorbeeldcode in te vullen.

ui <- fluidPage(
  titlePanel('BMI Calculator'),
  sidebarLayout(
    sidebarPanel(
      numericInput('height', 'Enter your height in meters', 1.5, 1, 2),
      numericInput('weight', 'Enter your weight in Kilograms', 60, 45, 120)
    ),
    mainPanel(
      textOutput("bmi"),
      textOutput("bmi_status")
    )
  )
)

server <- function(input, output, session) {
  rval_bmi <- reactive({
    input$weight/(input$height^2)
  })
  # CODE BELOW: Add a reactive expression rval_bmi_status to 
  # return health status as underweight etc. based on inputs
  
  
  
  
  output$bmi <- renderText({
    bmi <- rval_bmi()
    paste("Your BMI is", round(bmi, 1))
  })
  output$bmi_status <- renderText({
    # MODIFY CODE BELOW: Replace right-hand-side with 
    # reactive expression rval_bmi_status
    bmi_status <- cut(rval_bmi(), 
      breaks = c(0, 18.5, 24.9, 29.9, 40),
      labels = c('underweight', 'healthy', 'overweight', 'obese')
    )
    paste("You are", bmi_status)
  })
}

shinyApp(ui = ui, server = server)

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