reactive change min/max range + 2 dataframes Shiny

Question

I have one problem with my Shiny app. Firstly, I have two dataframes in which there are two numeric columns ( number and number2). I also have dynamic ui sliderInput. Shiny app works fine till... when I choose Item dataframe, choose number in Y-axis variable and set range in sliderInput between e.g. 15 and 18, and after that I want to change Y-axis variable to number2 I get an error:
Error in eval(substitute(expr), envir, enclos) : wrong result size (2), expected 0 or 1
I know that the problem is caused because number in number2 column is between 1 and 10 and previous settings does not included that numbers. Could anyone tell me how to improve it?

ui.R

library(ggvis)

shinyUI(fluidPage(

titlePanel(""),

sidebarLayout(
 sidebarPanel(
  radioButtons("dataset", label = h4("Choose dataframe"),
               choices = list("Item" = "df1", "Task" = "df2")),
   selectInput("yvar", "Y-axis variable", axis_vars_y, selected = "number"),
   uiOutput("slider")
   ),
mainPanel(
  ggvisOutput("plot")
  )
 )
))

server.R

library(shiny)
library(dplyr)
library(magrittr)
library(lazyeval)

df1_number <-sample(seq(1,20,0.01),20,replace = T)
df2_number <-sample(seq(1,20,0.01),20,replace = T)
df1_number2 <-sample(seq(1,10,0.01),20,replace = T)
df2_number2 <-sample(seq(1,10,0.01),20,replace = T)

df1 <- data.frame(name = rep(letters[1:4],each = 5), number = df1_number, number2 = df1_number2)
df2 <- data.frame(name = rep(letters[1:4],each = 5), number = df2_number, number2 = df2_number2)
axis_vars_y <- c("number" = "number", "number2" = "number2")



shinyServer(function(input, output) {

  datasetInput <- reactive({
    switch(input$dataset,
           df1 = df1,
           df2 = df2)
  })

  axis_vara_y <- reactive({
    switch(input$yvar,
           number = 2,
           number2 = 3)
  }) 

    output$slider <- renderUI({
      sliderInput("inslider","Slider", min   = min(datasetInput()[,axis_vara_y()]), 
                                       max   = max(datasetInput()[,axis_vara_y()]),
                                       value = c(min(datasetInput()[,axis_vara_y()]), 
                                                 max(datasetInput()[,axis_vara_y()])),
                                       step = 0.5)
})

  data <- reactive({
    filteredData <- datasetInput()
    if(!is.null(input$inslider)){
      filteredData <- filteredData %>%
        filter(filteredData[,axis_vara_y()] >= input$inslider[1],
               filteredData[,axis_vara_y()] <= input$inslider[2])
    }
    filteredData
})

  data_two <- reactive({
    data() %>%
      mutate(id = 1:n())

  })  

  vis <- reactive({

    yvar_name <- names(axis_vars_y)[axis_vars_y == input$yvar]
    yvar <- prop("y", as.symbol(input$yvar))

    data_two %>%
      ggvis(x = ~name, y = yvar) %>%    
      layer_points(size := 120,
                     fill = ~name,
                     fillOpacity := 0.6, 
                     key := ~id)

      })
      vis %>% bind_shiny("plot")
    })

Update---------------------------------------------------------------------------------------------------

The same error occurs when I set a range which does not included any value from number column (e.g. between 13 and 14).

Answer 1

As you realize, you are getting the error because the filtered dataset has no rows. A simple workaround would be to return the full dataset. This will reset the inputSlider for you to continue working without error. You only need to change your reactive data function.

data <- reactive({
  filteredData <- datasetInput()
  axisData <- axis_vara_y()

  if(!is.null(input$inslider)){
    filteredData <- filteredData %>%
      filter(filteredData[,axisData] >= input$inslider[1],
             filteredData[,axisData] <= input$inslider[2])
  }

  # the new part to reset the slider
  if(nrow(filteredData) == 0){
    return(datasetInput())
  }else{
    return(filteredData)
  }
})

I have taken the liberty of simplifying the code a little bit as you can assign your reactive data statements and not have the shiny app call them several times.