Shiny sliderInput showing duplicate values

Question

I have an issue with sliderInput. In my app, when a user loads data (actionBTTN) the years of my sliderInput get updated (with updateSliderInput) according to that data. But I have noticed that for data containing few years (4-5) the sliderInput would show repeated years. I also noticed, that it seems to only happens when my screen size is bigger.

Here is how it looks with a small sized window: no duplicated year values, how I would like it to be in the app And here is how it looks with a larger window: duplicated year values

Here is an example of my app:

library(shiny)
library(shinyWidgets)

ui <- fluidPage(
  sidebarLayout(
    sidebarPanel(
      # initial input with no years selected, it will update once data is loaded
      sliderInput(
        inputId = "years", 
        label = "Choose a time range:", 
        min = 0, max = 1, 
        value = c(0,1), 
        #dragRange = TRUE, 
        step = 1, 
        sep = ''
      ),
      actionBttn(
        inputId = "load_data",
        label = "Get data!",
        color = "primary",
        style = "fill", 
        icon = icon("arrow-alt-circle-down"),
        size = "xs",
        block = TRUE
      )
    ),
    mainPanel()
  )
)

server = function(input, output, session) {
  observeEvent(input$load_data, {
    mydata <- data.frame(numbers = c(1:5), year = c(2010:2014))
    
    minim = min(mydata$year)
    maxim = max(mydata$year)
    
    updateSliderInput(session, inputId = "years",
                      min = minim, max = maxim, 
                      value = c(minim, maxim),
                      # calculate step dynamically (@Isa's idea)
                      step = seq(minim, maxim, length.out = length(mydata$year))[2] - seq(minim, maxim, length.out = length(mydata$year))[1])
  })
}

shinyApp(ui, server)

I have already tried changing the step and sep arguments, also seting mydata$year as integer. Has anybody encountered the same issue? All help is welcome.

Thanks :)

Answer 1

Maybe this is what you were expecting

mydata <- data.frame(numbers = c(1:6), year = c(2010:2015))

library(shiny)
library(shinyWidgets)

ui <- fluidPage(
  sidebarLayout(
    sidebarPanel(
      # initial input with no years selected, it will update once data is loaded
      sliderInput(
        inputId = "years", 
        label = "Choose a time range:", 
        min=0, max=1, 
        value = 0, 
        dragRange = TRUE, 
        step = seq(0, 1, length.out = length(mydata$year))[2] - seq(0, 1, length.out = length(mydata$year))[1], 
        # step = 0.2, # Above step calculates dynamically
        sep = ''
      ),
      actionBttn(
        inputId = "load_data",
        label = "Get data!",
        color = "primary",
        style = "fill", 
        icon = icon("arrow-alt-circle-down"),
        size = "xs",
        block = TRUE
      )
    ),
    mainPanel()
  )
)

server = function(input, output, session) {
  observeEvent(input$load_data, {
    min = min(mydata$year)
    max = max(mydata$year)

    updateSliderInput(session, inputId = "years",
                      min = min, max = max, 
                      value = min, step = 1)
  })
}

shinyApp(ui, server)

Reason behind updateSliderInput repeating the values was to fill the number of ticks generated by sliderInput in ui object when argument ticks is passed as TRUE.

Behind the scene code of sliderInput for number of ticks:

range <- max - min
if (ticks) {
    n_steps <- range/step
    scale_factor <- ceiling(n_steps/10)
    n_ticks <- n_steps/scale_factor
}
else {
    n_ticks <- NULL
}

You can check the whole working of any function by keeping the cursor on function and pressing f2 in windows.

So if we want the values not to repeat then number of ticks should be equal to number of distinct values of the variable in consideration.