populating selectInput based on another selectInput

Question

I've read similar questions on Stack Overflow but do not seem to be able to get my code to work correctly. I've reduced this to a reprex.

I'm trying to allow the user to select a table, and based on that table, select one of the columns associated with the selected table.

One problem I see is that there's no way to immediately populate the column selector (before choosing a table from the table selector) when the app launches. Also, the column selector is simply not populating with columns no matter what I do. Thanks for any help you can give me.

library(shiny)

tables <- c("A", "B", "C")
columns <- list(A = c("a1", "a2", "a3"), B = c("b1", "b2"), C = c("c1", "c2", "c3", "c4"))

# Define UI for application that draws a histogram
ui <- fluidPage(
  
  # Application title
  titlePanel("Old Faithful Geyser Data"),
  
  # Sidebar with a slider input for number of bins 
  sidebarLayout(
    sidebarPanel(
      selectInput(inputId = "table_selector", label = "Tables", choices = tables, selected = "A"),
      selectInput(inputId = "column_selector", label = "Columns", choices = "")),
    
    # Show a plot of the generated distribution
    mainPanel(
      textOutput("selected_table"),
      textOutput("selected_columns")
    )
  )
)

# Define server logic required to draw a histogram
server <- function(input, output) {
  rv <- reactiveValues("selected_cols" = unlist(columns$A))

  observeEvent(input$selected_table_selector, {
    message("Table event observed")
    rv$selected_cols <- selected_table[input$table_selector()]
    updateSelectInput("column_selector", choices = rv$selected_cols())
  })
  
  # Will use the following two query a database
  output$selected_table <- renderText({paste(input$table_selector)})
  output$selected_columns <- renderText({rv$selected_cols})
}

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

score 0 · Answer 1 · answered Jan 21 '22 at 23:03

You have many syntax issues. Try this

library(shiny)

tables <- c("A", "B", "C")
columns <- list(A = c("a1", "a2", "a3"), B = c("b1", "b2"), C = c("c1", "c2", "c3", "c4"))

# Define UI for application that draws a histogram
ui <- fluidPage(
  
  # Application title
  titlePanel("Old Faithful Geyser Data"),
  
  # Sidebar with a slider input for number of bins 
  sidebarLayout(
    sidebarPanel(
      selectInput(inputId = "table_selector", label = "Tables", choices = tables, selected = "A"),
      selectInput(inputId = "column_selector", label = "Columns", choices = "")),
    
    # Show a plot of the generated distribution
    mainPanel(
      textOutput("selected_table"),
      verbatimTextOutput("selected_columns")
    )
  )
)

# Define server logic required to draw a histogram
server <- function(input, output,session) {
  #rv <- reactiveValues(selected_cols = NULL)
  
  observeEvent(input$table_selector, {
    message("Table event observed")
    choices <- columns[[input$table_selector]]
    updateSelectInput(session, "column_selector", choices = choices )
  })
  
  # Will use the following two query a database
  output$selected_table <- renderText({paste(input$table_selector)})
  output$selected_columns <- renderPrint({input$column_selector})
}

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

Your code works perfectly. I had forgotten you can use [[ ]] to unlist the list's element. The solution is simpler than I expected. Thanks! — wdchild, Jan 24 '22 at 23:05

populating selectInput based on another selectInput

1 Answers1