How to dynamically populate dropdown box choices in shiny dashboard - r

Question

I am developing one app in shiny dashboard in that I want to dynamically populate dropdown box once csv is uploaded. Dropdown will contain top 10 cities by user registrations which I get from following code.
final_data %>%
group_by(registrant_city) %>%
summarise(Total = n()) %>%
arrange(desc(Total)) %>%
top_n(n = 10)
These cities should go into dropdown box.
tabItem("email",
fluidRow(
box(
width = 4, status = "info",solidHeader = TRUE,
title = "Send Emails",
selectInput("email_select",
"Select Email Content",
choices = c("Price" = "price",
"Services" = "service"
)),
selectInput("cities",
"Select City",
choices = ??
))
))
Please help..

Answer 1

Use updateSelectInput in your server like below and set choices = NULL in your ui :
function(input, output, session) {
# If this isn't reactive you can put it in your global
choices_cities <- final_data %>%
group_by(registrant_city) %>%
summarise(Total = n()) %>%
arrange(desc(Total)) %>%
top_n(n = 10)
updateSelectInput(session = session, inputId = "cities", choices = choices_cities$registrant_city)
}
Or if final_data is reactive something like this :
function(input, output, session) {
choices_cities <- reactive({
final_data %>%
group_by(registrant_city) %>%
summarise(Total = n()) %>%
arrange(desc(Total)) %>%
top_n(n = 10)
})
observeEvent(choices_cities(), {
updateSelectInput(session = session, inputId = "cities", choices = choices_cities()$registrant_city)
})
}
A working example :
library("dplyr")
library("shiny")
data("world.cities", package = "maps")
ui <- fluidPage(
sliderInput(inputId = "n", label = "n", min = 10, max = 30, value = 10),
selectInput(inputId = "cities", label = "Select City", choices = NULL)
)
server <- function(input, output, session) {
choices_cities <- reactive({
choices_cities <- world.cities %>%
arrange(desc(pop)) %>%
top_n(n = input$n, wt = pop)
})
observe({
updateSelectInput(session = session, inputId = "cities", choices = choices_cities()$name)
})
}
shinyApp(ui = ui, server = server)

Answer 2

I got the answer for above. Here is what I did.
ui.R
uiOutput("city_dropdown")
And my server.R looks like following
output$city_dropdown <- renderUI({
city <- reg_city(final_data)
city <- city$registrant_city
city <- as.list(city)
selectInput("email_select",
"Select Email Content",
choices = city
)
})
reg_city() gives me the top 10 cities which I want to populate into drop down box,then converting it to a list gives me desired output.