基于另一个selectInput填充selectInput

Question

我读过类似的关于堆栈溢出的问题，但似乎无法让我的代码正确工作。我已经把这个简化成了重装。

我试图允许用户选择一个表，并在该表的基础上选择一个与所选表相关联的列。

我看到的一个问题是，当应用程序启动时，无法立即填充列选择器(在从表选择器中选择表之前)。而且，不管我做什么，列选择器都不会填充列。谢谢你能帮我的忙。

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)

Answer 1

您有许多语法问题。尝尝这个

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)