Dealing with nested selectizeInputs and modules - r

Question

I am having trouble with nested selectizeInputs, i.e. a group of select inputs where the selection in the first determines the choices in the second, which control the choices in the third, and so on.
Let's say I have an select1 that lets you choose a dataset, and select2 which lets you pick a variable in the dataset. Obviously the choices in select2 depend on the selection in select1. I find that if a user selects a variable from select2, and then changes select1, it doesn't immediately wipe out the value from select2, but instead it goes through a reactive sequence with the new value in select1, and the old value from select2, which is suddenly referencing a variable in a different dataset, which is a problem.
Example:
library(shiny)
ui =fluidPage(
selectizeInput('d',choices=c('mtcars','iris'),
label="Datasets"),
uiOutput("vars"),
htmlOutput("out")
)
server = function(input, output, session) {
output$vars <- renderUI({
req(input$d)
selectizeInput("v",choices=names(get(input$d)), label="Variables",
options=list(onInitialize=I('function() {this.setValue("");}')))
})
output$out <- renderUI({
req(input$d,input$v)
HTML(paste0("The max is ",max(get(input$d)[[input$v]])))
})
}
runApp(list(ui = ui, server = server))
On launch, select mpg, and displays max value.
Now, after selecting mpg, if you switch to iris, you will get a barely noticeable error, then it corrects itself. This is a toy example, so the error is insignificant, but there could easily be cases where the error is much more dire (as is the case with the app I am currently developing).
Is there a way to handle nested selectizeInputs such that changes in an upstream selectizeInput won't evaluate with old values of down stream selectizeInputs when changed?
Thanks
edit: This issue turns out to have to do more with modules than anything else I believe:
library(shiny)
library(DT)
testModUI <- function(id) {
ns <- NS(id)
DT::dataTableOutput(ns("out"))
}
testMod <- function(input, output, session, data) {
output$out <- DT::renderDataTable({
data()
},caption="IN MODULE")
}
ui =fluidPage(
selectizeInput('d',choices=c('mtcars','iris'),
label="Datasets"),
uiOutput("vars"),
testModUI("test"),
DT::dataTableOutput("test2")
)
server = function(input, output, session) {
output$vars <- renderUI({
req(input$d)
selectizeInput("v",choices=names(get(input$d)), label="Variables",
options=list(onInitialize=I('function() {this.setValue("");}')))
})
observe({
req(input$d,input$v)#,get(input$d)[[input$v]])
validate(
need(input$v %in% names(get(input$d)), 'Wait.')
)
callModule(testMod,"test",reactive(data.frame(v1=max(get(input$d)[[input$v]]))))
})
output$test2 <- DT::renderDataTable({
req(input$d,input$v)#,get(input$d)[[input$v]])
validate(
need(input$v %in% names(get(input$d)), 'Wait.')
)
data.frame(v1=max(get(input$d)[[input$v]]))
},caption="OUTSIDE MODULE")
}
runApp(list(ui = ui, server = server))

Answer 1

Hello you can put condition to check if your code is going to run, here you just need that input$v to be a valid variable from input$d, so do :
output$out <- renderUI({
req(input$d,input$v)
if (input$v %in% names(get(input$d))) {
HTML(paste0("The max is ",max(get(input$d)[[input$v]])))
}
})
# or
output$out <- renderUI({
req(input$d,input$v)
validate(
need(input$v %in% names(get(input$d)), 'Wait.')
)
HTML(paste0("The max is ",max(get(input$d)[[input$v]])))
})
EDIT with module, you can define your module with an expression to validate like this :
testMod <- function(input, output, session, data, validExpr) {
output$out <- DT::renderDataTable({
validate(need(validExpr(), FALSE))
data()
},caption="IN MODULE")
}
And call the module in the server with the expression in a function :
observe({
req(input$d,input$v)
callModule(
module = testMod,
id = "test",
data = reactive({ data.frame(v1=max(get(input$d)[[input$v]])) }),
validExpr = function() input$v %in% names(get(input$d))
)
})