R Shiny: Conditional formatting selectInput items

Question

When we have a all missing columns in the data frame, typically we don't want the user to select them to plot. There are many ways to do this but is it possible to let the items in the selectInput have conditional colors.

For example, how to let all missing column names (like the var2 column in my sample code) in the selectInput item list go grey. In other words, how to rewrite the selectInput for us to pass in a indicator vector for the conditional formatting.

library(shiny)

server <- function(input, session, output) {

  DATA = data.frame(var1 = c(2,3,4,1,5), var2 = c(NA,NA,NA,NA,NA))

  output$select_1 = renderUI({
    variables = names(DATA)
    selectInput("select_input","select", choices = variables)

    # is.all.na.indicator = sapply(DATA, function(x) all(is.na(x))) 
    # selectInput("select_input","select", choices = variables, goGrey = is.all.na.indicator)
  }) 
}

ui <- fluidPage(
    uiOutput("select_1")
)

shinyApp(ui = ui, server = server)

Answer 1

library(shiny)

server <- function(input, session, output) {

  DATA <- data.frame(var1 = c(2,3,4,1,5), var2 = c(NA,NA,NA,NA,NA))

  output$select_1 <- renderUI({
    variables <- variableNames <- names(DATA)
    emptyColumns <- which(sapply(DATA, function(x) all(is.na(x))))
    for(i in emptyColumns){
      variableNames[i] <- 
        sprintf("<span style='color:red;'>%s</span>", variables[i])
    }
    selectizeInput("select_input", "select", 
                   choices = setNames(variables, variableNames), 
                   options = list(render = I("
  {
    item: function(item, escape) { return '<div>' + item.label + '</div>'; },
    option: function(item, escape) { return '<div>' + item.label + '</div>'; }
  }")))
  }) 
}

ui <- fluidPage(
  uiOutput("select_1")
)

shinyApp(ui = ui, server = server)