R Shiny selectInput开启多选后报Error in if参数长度为零错误

错误原因 #

开启multiple = TRUE的下拉框在未完成选择时，对应的input值为长度为0的空向量，直接放入if条件判断就会触发「argument is of length zero」报错；另外多选场景下输入值可能是长度大于1的向量，直接用!=做判断会返回多值逻辑向量，不符合if仅支持单逻辑值的要求。

修复方案 #

需要调整3部分逻辑：

• 给多选下拉框设置初始默认选中值为"All"，避免初始空值状态
• 所有if判断先校验输入非空，再判断选中值中是否包含"All"，适配多值场景
• 过滤逻辑中如果选中项包含"All"，直接跳过该维度的过滤操作

修复后完整可运行代码 #

library(shiny)
library(DT)

State <- c("NV", "NV","NV", "MD", "MD", "MD", "MD", "NY", "NY", "NY", "OH", "OH", "OH")
County <- c("CLARK", "WASHOE", "EUREKA", "MONTGOMERY", "HOWARD", "BALTIMORE", "FREDERICK", "BRONX", "QUEENS", "WESTCHESTER", "FRANKLIN", "SUMMIT", "STARK" )
City <- c("Las Vegas", "Reno", "Eureka", "Rockville", "Columbia", "Baltimore", "Thurmont", "Bronx", "Queens", "Yonkers", "Columbus", "Akron", "Canton")
Rating<- c(1,2,3,4,5,6,7,8,9,10,11,12,13)
df <- data.frame(State, County, City, Rating, stringsAsFactors = F)

ui <- fluidPage(
  titlePanel("Test Dashboard "),
  sidebarLayout(
    sidebarPanel(
      selectInput("data1", "Select State", choices = c("All", unique(df$State))),
      selectInput("data2", "Select County", choices = NULL, multiple = TRUE),
      selectInput("data3", "select City", choices = NULL, multiple = TRUE)
    ),
    mainPanel(
      DTOutput("table")
    )
  ))

server <- function(input, output, session){
  
  observeEvent(input$data1, {
    if (!"All" %in% input$data1) {
      updateSelectInput(session, "data2", "Select County", 
                        choices = c("All", unique(df$County[df$State %in% input$data1])),
                        selected = "All")
    } else {
      updateSelectInput(session, "data2", "Select County", 
                        choices = c("All", unique(df$County)),
                        selected = "All")
    }
  }, priority = 2)
  
  observeEvent(c(input$data1, input$data2), {
    req(input$data2)
    if (!"All" %in% input$data2) {
      updateSelectInput(session, "data3", "Select City", 
                        choices = c("All", unique(df$City[df$County %in% input$data2])),
                        selected = "All")
    } else {
      if (!"All" %in% input$data1) {
        updateSelectInput(session, "data3", "Select City", 
                          choices = c("All", unique(df$City[df$State %in% input$data1])),
                          selected = "All")
      } else {
        updateSelectInput(session, "data3", "Select City", 
                          choices = c("All", unique(df$City)),
                          selected = "All")
      }
    }
  }, priority = 1)
  
  filtered_data <- reactive({
    req(input$data2, input$data3)
    temp_data <- df
    if (!"All" %in% input$data1) {
      temp_data <- temp_data[temp_data$State %in% input$data1, ]
    }
    if (!"All" %in% input$data2) {
      temp_data <- temp_data[temp_data$County %in% input$data2, ]
    }
    if (!"All" %in% input$data3) {
      temp_data <- temp_data[temp_data$City %in% input$data3, ]
    }
    temp_data
  })
  
  output$table <- renderDT(
    filtered_data()
  )
  
}

shinyApp(ui, server)

内容的提问来源于stack exchange，提问作者wizkids121