CODEWITHSUNDEEP
rshiny
emehex
emehex

Reputation: 10538

Constraining a shiny app input based on another input

I have a basic shiny app that evaluates A + B:

library(shiny)

ui <- fluidPage(
    numericInput(inputId = "A", label = "A", value = 5, step = 1),
    sliderInput(inputId = "B", label = "B", min = 0, max = 10, value = 5),
    textOutput(outputId = "value")
)

server <- function(input, output) {
    output$value <- renderText(paste0("A + B = ", input$A + input$B))
}

shinyApp(ui = ui, server = server)

A is a numericInput value and B is a sliderInput value.

I want to constrain my app so that the maximum input value for B is always 2 * A. I, therefore, must change the hardcoded max = in sliderInput to something that can be dynamic. How can I accomplish this?

Thanks

Upvotes: 4

Views: 4696

Answers (2)

HubertL
HubertL

Reputation: 19544

You can call updateSliderInput to change the maximum value for B from within an observe which will be triggered whenever A changes:

library(shiny)

ui <- fluidPage(
  numericInput(inputId = "A", label = "A", value = 5, step = 1),
  sliderInput(inputId = "B", label = "B", min = 0, max = 10, value = 5),
  textOutput(outputId = "value")
)

# Notice the session argument to be passed to updateSliderInput
server <- function(input, output, session) {
  output$value <- renderText(paste0("A + B = ", input$A + input$B))
  observe(updateSliderInput(session, "B", max = input$A*2))
}

shinyApp(ui = ui, server = server)

Upvotes: 11

Tonio Liebrand
Tonio Liebrand

Reputation: 17689

You are looking for renderUI()

library(shiny)

ui <- fluidPage(
  numericInput(inputId = "A", label = "A", value = 5, step = 1),
  uiOutput("slider"),
  textOutput(outputId = "value")
)

server <- function(input, output) {
  output$value <- renderText(paste0("A + B = ", input$A + input$B))
  output$slider <- renderUI({
    sliderInput(inputId = "B", label = "B", min = 0, max = 2*input$A, value = 5)
  })
}

shinyApp(ui = ui, server = server)

Upvotes: 6

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