R Shiny Reactive values, dplyr filter error?

问题

I am trying to figure out as I select input in UI to immediately reflect the results on page. My search results led me to look into reactive expression and reactive values. But as I am trying to filter the value on data, I think it is causing some complication yet I have no clue what I am supposed to do with this.

It seems like the filter function doesn't seem to work though.

This is the error message:

Warning: Error in UseMethod: no applicable method for 'filter_' applied to an object of class "c('reactiveExpr', 'reactive')"
Stack trace (innermost first):
    51: filter_
    50: filter.default
    49: filter
    48: function_list[[i]]
    47: freduce
    46: _fseq
    45: eval
    44: eval
    43: withVisible
    42: %>%
    41: eval
    40: makeFunction
    39: exprToFunction
    38: observe
    37: server 
     1: runApp
Error in UseMethod("filter_") : 
  no applicable method for 'filter_' applied to an object of class "c('reactiveExpr', 'reactive')"

回答1:

I found two problems,

first reactive statements are functions - you need to add brackets () after them. second, you need to work on the naming of your variables, especially naming an variable data is never a good thing in R and you are naming two objects the same first the data set itself and second the reactive statement returning the dataset - it seemed like this confused shiny quite a lot. I renamed the reactive statement to dta and that solved it for me. Here is the complete server code

server <- function(input, output, session) {

  dta <- reactive({
    data
  })

  output$p1 <- renderText({
    paste0("You currently live in ", input$Location, " and are contemplating a job offer in ", input$reLocation, ".")
  })

  values <- reactiveValues()
  observe({ 
    # req(input$Location,input$reLocation)
    # browser()
    values$LocationCost <-  dta() %>% filter(UrbanArea == input$Location) %>% select(CostOfLivingIndex)
    values$reLocationCost <-  dta() %>% filter(UrbanArea == input$reLocation) %>% select(CostOfLivingIndex)
  }) 
  # observeEvent(input$Location, {
  #   values$LocationCost <- data %>%
  #     filter(UrbanArea == input$Location) %>%
  #     select(CostOfLivingIndex)
  # })
  # 
  # observeEvent(input$reLocation, {
  #   values$reLocationCost <- data %>%
  #     filter(UrbanArea == input$reLocation) %>%
  #     select(CostOfLivingIndex)
  # })

  output$p2 <- renderText({
    if (values$LocationCost < values$reLocationCost) {
      calc <- round(100* ((values$reLocationCost-values$LocationCost)/values$LocationCost), 2)
      print(paste0("You need ", calc, "% increase in your after-taxes income in order to maintain your present lifestyle."))
    } else {
      calc <- round(100 * ((values$LocationCost-values$reLocationCost)/values$reLocationCost), 2)
      print(paste0("You can sustain upto ", calc, "% reduction in after taxes income without reducing your present lifestyle."))
    }
  })


} 

Hope this helps!!

来源：https://stackoverflow.com/questions/53588091/r-shiny-reactive-values-dplyr-filter-error