How to make a function in a for loop or lapply loop in a tabItem dashboard shiny

Question

I'm making a ShinyDashboard program and I have some troubles in finding a way to make a loop in the dashboardBody to catch MenuItems. This is a simple example of what I'm trying to fix:

library(shiny)
library(shinyjs) 
library(shinydashboard)

VecNames=c("A","B","C","D","E")

ui <- dashboardPage(
dashboardHeader(title = "My Page"),
dashboardSidebar(sidebarMenuOutput("sideBar_menu_UI")),
dashboardBody(
uiOutput("body_UI"),
uiOutput("test_UI")
) 
)

server <- shinyServer(function(input, output, session) { 
output$sideBar_menu_UI <- renderMenu({
sidebarMenu(id = "sideBar_Menu",
            menuItem("Menu 1", tabName="menu1_tab", icon =       icon("calendar"),
                     lapply(1:length(VecNames), function(i) {
                       menuSubItem(VecNames[i], tabName = VecNames[i]  ,icon = icon("angle-right"))
                     })
                     ),
            menuItem("Menu 2", tabName="menu2_tab", icon =  icon("database"))
 )
 }) 
output$test_UI <- renderUI ({
A=tabItems(
  tabItem(tabName = "menu1_tab", uiOutput("menu1_UI")),    



 #      lapply(1:5, function(i){
 #        tabItem(tabName = VecNames[i], uiOutput(paste0("Menu",i)))        
 #      }),
  tabItem(tabName = VecNames[1], uiOutput(paste0("Menu",1))),
  tabItem(tabName = VecNames[2], uiOutput(paste0("Menu",2))),
  tabItem(tabName = VecNames[3], uiOutput(paste0("Menu",3))),
  tabItem(tabName = VecNames[4], uiOutput(paste0("Menu",4))),
  tabItem(tabName = VecNames[5], uiOutput(paste0("Menu",5))),      


  tabItem(tabName = "menu2_tab", uiOutput("menu2_UI"))
 )
 })
 output$body_UI <- renderUI ({
 p("Default content in body outsite any sidebar menus.")
 })
 output$menu1_UI <- renderUI ({
 box("Menu 1 Content")
 })
 output$menu2_UI <- renderUI ({
 box("Menu 2 Content")
 })

 lapply(1:5, function(i){
 output[[paste0("Menu",i)]]<- renderUI({
  box(paste0("Menu",i))
  })
  })

   })

 runApp(list(ui= ui, server = server))

I want something like the following code but it seems that lapply doesn't accept tabItem as a function

  #      lapply(1:5, function(i){
  #        tabItem(tabName = VecNames[i], uiOutput(paste0("Menu",i)))        
  #      })

Any help? Thank you for your answers on advanced

Answer 1

The problem in your code is, that you try to use a list of tabItem objects as an argument for tabItems, but this is invalid according to the documentation of tabItems.

tabItems(...)

... Items to put in the container. Each item should be a tabItem.

do.call can be used to resolve this issue. Basically, do.call operates as follows.

add <- function(x, y){x + y}
do.call(add, list(4, 3)) # same as add(4, 3)
## 7

So you basically want to use the list returned from lapply as the second argument to do.call while the first argument is the function to call (tabItems).

output$test_UI <- renderUI ({
  items <- c(
    list(tabItem(tabName = "menu1_tab", uiOutput("menu1_UI"))),
    lapply(1:5, function(i){
      tabItem(tabName = VecNames[i], uiOutput(paste0("Menu",i)))        
    })
  )
  do.call(tabItems, items)
})