CODEWITHSUNDEEP
rshiny
Steven Ouellette
Steven Ouellette

Reputation: 131

How can I trigger an output when a value changes in a different output?

I have an output that takes user input to select which of a number of calculations to use and results in 5 numbers. That output pushes out the results of this and other calculations as an HTML table. The individual calculations are not particularly complicated, but user selections choose which of many approaches they are using, so I don't really want to replicate all that code in other outputs that are going to use just those 5 numbers.

My thought was to use the double-arrow to make those numbers available to the other outputs (in my case some plots). My goal is to generate graphs from numbers already generated in a different output, however that gets accomplished. I am not attached to the approach below, it is just where I am right now.

I ran into a number of problems just using <<- and tried a lot of things to get it to work. I won't complicate this further with all the things I tried and the problems they created.

The MRE below replicates this by calculating a number in one output that is then to be used in another output. If you enter different numbers of bins, the second output is never triggered to update to the new number. For this MRE I could of course directly use the user input to calculate that number but that is what I am trying to avoid in the real app. I also don't want to use a "Go!" button if I can avoid it since part of the fun is watching how things change in response to your various selections.


# Define UI for application that draws a histogram
ui <- fluidPage(

    # Application title
    titlePanel("Old Faithful Geyser Data"),

    # Sidebar with a slider input for number of bins 
    sidebarLayout(
        sidebarPanel(
            numericInput("bins",
                        "Number of bins:",
                        min = 1,
                        max = 50,
                        value = 30)
        ),

        # Show a plot of the generated distribution
        mainPanel(
           plotOutput("distPlot"),
           textOutput("binnum")
        )
    )
)

# Define server logic required to draw a histogram
server <- function(input, output) {
    a_number<-0

    output$distPlot <- renderPlot({
                # generate bins based on input$bins from ui.R
        x    <- faithful[, 2]
        
        bins <- seq(min(x), max(x), length.out = input$bins + 1)
        
        a_number<<-bins[2]/5}

        # draw the histogram with the specified number of bins
        hist(x, breaks = bins, col = 'darkgray', border = 'white')
    })
    
    output$binnum<-renderText({
        
        a_number
    })
}

# Run the application 
shinyApp(ui = ui, server = server)

Upvotes: 1

Views: 203

Answers (1)

DaveArmstrong
DaveArmstrong

Reputation: 21992

Could you just treat bins and a_number as reactive?


# Define UI for application that draws a histogram
ui <- fluidPage(
  
  # Application title
  titlePanel("Old Faithful Geyser Data"),
  
  # Sidebar with a slider input for number of bins 
  sidebarLayout(
    sidebarPanel(
      numericInput("bins",
                   "Number of bins:",
                   min = 1,
                   max = 50,
                   value = 30)
    ),
    
    # Show a plot of the generated distribution
    mainPanel(
      plotOutput("distPlot"),
      textOutput("binnum")
    )
  )
)

# Define server logic required to draw a histogram
server <- function(input, output) {
  #  a_number<-0
  # generate bins based on input$bins from ui.R
  data(faithful)
  x    <- faithful[, 2]
  bins <- reactive({
    seq(min(x), max(x), length.out = input$bins + 1)
  })
  a_number <- reactive({
    req(bins())
    -bins()[2]/5
  })
  output$distPlot <- renderPlot({
    
    # draw the histogram with the specified number of bins
    hist(x, breaks = bins(), col = 'darkgray', border = 'white', xlab = paste0("a = ", -bins()[2]/5))
  })
  
  output$binnum<-renderText({
    
    a_number()
  })
}

# Run the application 
shinyApp(ui = ui, server = server)

Upvotes: 1

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