How to make related server-side selectize UI elements in R Shiny application?

Question

I have R Shiny application with two UI selectors where each one has a big list of items. I know how to make server-side element for one element. But how to make two related server-side 'selectInput' elements. So, when exist a change in one element - another should reflect appropriately.

Example.

1. The first list has 97,310 elements.

2. The second list should have:

2.1. for 1st element "Aaban" - 2 related values (10, 11)

2.2. for 2nd element "Aabha" - 1 related value (12)

2.3. for 3rd element "Aabid" - 3 related values (13, 14, 15)

Here is R code.

library(shiny)
library(dplyr)
library(babynames)

# 1. Data sets

# 1.1. First data set (list)
list_names <- babynames::babynames %>% 
  distinct(name) %>%
  pull(name) %>%
  sort()

# 1.2. Second data set (data frame) for 3 first 'names' elements
df_ages <- data.frame(
  name = c("Aaban", "Aaban", "Aabha", "Aabid", "Aabid", "Aabid"),
  age  = c(10, 11, 12, 13, 14, 15))

# 2. UI
ui <- fluidPage(
  fluidRow(selectInput("si_name", "Name", multiple = FALSE, choices = character(0))),
  fluidRow(selectInput("si_age", "Age", multiple = FALSE, choices = character(0))))

# 3. Server
server <- function(input, output, session) {
  updateSelectizeInput(session, "si_name", choices = list_names, server = TRUE)
  updateSelectizeInput(session, "si_age", choices = df_ages$age, server = TRUE)
}

# 4. App
shinyApp(ui, server)

Thanks!

Answer 1

I think you want:

# 2. UI
ui <- fluidPage(
  fluidRow(selectInput("si_name", "Name", multiple = FALSE, 
                       choices = unique(df_ages$name))),
  fluidRow(selectInput("si_age", "Age", multiple = FALSE, choices = character(0)))
)

# 3. Server
server <- function(input, output, session) {

  observeEvent(input$si_name, {
    ages <- df_ages[df_ages$name == input$si_name, "age"]
    updateSelectizeInput(session, "si_age", choices = ages, server = TRUE)
  })

}