How to compute value for InputSlider R Shiny?

Question

I'm doing a Shiny app and I have a question. I want to have a slider input which min and max values depends on values in some dataframe. That's easy to make. But I want the value of slider input to be mean of those min and max values in input and don't know how to data. I don't know if anyone will understand but maybe code will help.
ui.R

sliderInput("param1", "Param1", min = 0, max = 1, value = 0, step = 0.01),

server.R

observeEvent( updateSliderInput(inputId = "param1", min = ... //getting the value from df,
                          max = ... //getting the value from df,
                          value = input$param1$min + (input$param1$max - input$param1$min/2)) //that's what I want to do but it's not working

Hope someone can help. Thanks!

Answer 1

As you haven't provided any reproducible demo and error information, I can only tell you what I found wrong.

The value argument in updateSliderInput() need to be The initial value of the slider, either a number, a date (class Date), or a date-time (class POSIXt). A length one vector will create a regular slider; a length two vector will create a double-ended range slider. Must lie between min and max..

In your case, the value is equal to input$param1$min/2 + input$param1$max, which is greater than input$param1$max.

Update

Based on the code you provided, I would like to mention several things.

1. shinyUI() and shinyServer() are superseded in the current version of Shiny. Although it doesn't generate any error, I would suggest you to not use them.

2. To use updateSliderInput(), you need input updater functions send a message to the client. Therefore, you should combine updateSliderInput() with some functions like observe() or observeEvent().

3. The value generated from the double-ended range slider is a vector of length two. You should use input$param1[1] instead of input$param1$min.

4. There's some reactivity problem in your code. I would suggest you to understand how shiny update the value. This link may be useful for this part.

I'm not very sure about what you want, but I would put what I understand you want below.

ui = fluidPage(
  navbarPage(title = "Title",              
             tabPanel("Section1", 
                      div("text"), 
             ),              
             tabPanel(
               "Section2", 
               sidebarPanel(
                 sliderInput(inputId = "param1", 
                             label = "SlideBar", 
                             min = min(iris$Sepal.Length), 
                             max = max(iris$Sepal.Length), 
                             value = min(iris$Sepal.Length)/2 + max(iris$Sepal.Length)/2), 
                 actionButton("submit", "Submit")
               ),
               mainPanel(h1('Text'))
             ) 
  )
)

server = function(input, output) { 
  observe({
    print(input$param1)
  })
}

shinyApp(ui = ui, server = server)