R Shiny updateSelectizeInput throwing error and not updating

Question

I am attempting to create two drop downs in shiny - one a list of states that then filters the second drop down which lists all counties for the selected state. The following code works BUT the counties do not update when you change states.

UI

pageWithSidebar(
 headerPanel("My chart"),
 sidebarPanel(
  uiOutput("sel_state"),
  uiOutput("sel_county")
 ),
 mainPanel(
  tableOutput("table")
 )
)

Server

function(input, output, session) {

  output$sel_state <- renderUI({
   selectizeInput('state', 'Select a State', choices=c("Choose One" = "", state_list))
  })

  output$sel_county <- renderUI({
   county_list <- reactive({
    df %>%
     filter(state == input$state) %>%
     pull(county) %>%
     sort() %>%
     as.character()
   })
    selectizeInput('county', 'Select a County', choices=c("Choose One" = "", county_list()))
  })

  tab <- reactive({
   df %>%
    filter(state == input$state) %>%
    filter(county == input$county)
  })

  output$table <- renderTable({
   tab()
  })
 }

I attempted to replace the 'selectizeInput' in the county drop down with the following 'updateSelectizeInput' but keep getting the following error

New Server line

updateSelectizeInput(session, 'county', 'Select a County', choices=c("Choose One" = "", county_list()))

ERROR: cannot coerce type 'environment' to vector of type 'character'

Code to create data frames - the county list is not a proper list yet

    x <- getURL("https://raw.githubusercontent.com/nytimes/covid-19-data/master/us-counties.csv")
    csv <- read.csv(text=x)
    df <- as.data.frame(csv)
    state_list <- c(levels(df$state))
    county_list <- subset(df, select = c(3,2))

dput output

dput(head(cl))
structure(list(state = c("Washington", "Washington", "Washington", 
"Illinois", "Washington", "California"), county = c("Snohomish", 
"Snohomish", "Snohomish", "Cook", "Snohomish", "Orange")), row.names = 
c(NA, 6L), class = "data.frame")

Answer 1

I don't have your state/county info (or its structure), but this small example accomplishes what I think you describe. Things to note:

You need to first make the select input UI element with selectizeInput and then you can update its contents with updateSelectizeInput. So you need both functions, but for this small reprex I created the updateSelectizeInput is not needed though so I may have mis-interpreted what you are wanting to do.

In this example the county selectInput is receiving a reactive object as its choices input based on subsetting the county list by the user state selection, so the county select input will update as the user switches between states.

I also wrapped the county input with a conditionalPanel - this input will only show if the user has selected a state with the state selectInput.

UPDATE* add 'req(length(input$state) > 0)' so the reactive does not execute in server until state selected

library(shiny)
library(tidyverse)

ui <- fluidPage(


    pageWithSidebar(
        headerPanel("My chart"),
        sidebarPanel(
            uiOutput("sel_state"),
            conditionalPanel(condition = "input.state.length > 0",

            uiOutput("sel_county")
            )
        ),
        mainPanel(

        )
    )
)


server <- function(input, output) {

    #create example of data structure
   df <- structure(list(state = c("Washington", "Washington", "Washington", 
                         "Illinois", "Washington", "California"), county = c("Snohomish", 
                                                                             "Snohomish", "Snohomish", "Cook", "Snohomish", "Orange")), row.names = 
              c(NA, 6L), class = "data.frame")
   #pull out unique state names
    state_list <- as.character(unique(df$state))

    #filter for counties only in desired state and pull column to vector 
    selected_state_counties <- reactive({
    req(length(input$state) > 0)
        df %>% 
            filter(state == input$state) %>% 
            pull(county) %>% 
            as.character()

    })

output$sel_state <- renderUI({
        selectizeInput('state', 'Select a State', choices=c("Choose One" = "", state_list))
    })

output$sel_county <- renderUI({
        selectizeInput('county', 'Select a County', choices=c("Choose One" = "", selected_state_counties()))
    })


}

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