R Shiny: create reactiveValues object with input$ values - r

Question

I would like to create a reactiveValues object in Shiny whose contents are defined the values contained in input widgets. I managed to do it, but my implementation seems to be unnecessarily clunky:
Create an empty reactiveValues object
Monitor when the value of input widgets changes with observeEvent
Assign values to the reactiveValues object using the non-reactive values from input widgets (isolate)
Here is an example:
ui <- fluidPage(
fluidRow(
column(2, radioButtons("main", label = "Main dish", choices = list("salad", "pasta"))),
column(2, radioButtons("desert", label = "Desert", choices = list("fruit", "cake"))),
column(8, actionButton("extra", "Louder!", style="background-color: #ffdb99"))
),
verbatimTextOutput("myorder")
)
server <- function(input, output, session) {
# 1. Create reactiveValues object
menuR <- reactiveValues()
# 2. Update values whenever widgets change
observeEvent(c(input$main, input$desert),
menuR[["meal"]] <- paste(c(isolate(input$main), isolate(input$desert)), collapse = " & ")
)
# 3. Perform operations on object values
observeEvent(input$extra,
menuR[["meal"]] <- paste0(toupper(menuR[["meal"]]), "!!!")
)
output$myorder <- renderText(menuR[["meal"]])
}
shinyApp(ui, server)
I would very much like to create the reactiveValues object directly like this (greatly simplifies the code above):
# Set values upon creation
menuR <- reactiveValues(meal = paste(c(input$main, input$desert), collapse = " & "))
which does not work because input$main is reactive...
I would have guessed that defining reactiveValues objects with values obtained from widgets would be a common thing to do.
Am I missing something?
Thanks for your help,
Hugo

Answer 1

You can do this by using reactive() instead of reactiveValues(). menuR is a reactive object that depends on the input values of main and desert. You can use it by calling menu() in your server code once it is defined. Also, this saves you from using isolate() as you can set the value of menu as a reactive object inside observeEvent().
library(shiny)
ui <- fluidPage(
fluidRow(
column(2, radioButtons("main", label = "Main dish", choices = list("salad", "pasta"))),
column(2, radioButtons("desert", label = "Desert", choices = list("fruit", "cake"))),
column(8, actionButton("extra", "Louder!", style="background-color: #ffdb99"))
),
verbatimTextOutput("myorder")
)
server <- function(input, output, session) {
menuR <- reactive({
paste(c(input$main, input$desert), collapse = " & ")
})
observeEvent(
input$extra,
menuR <- reactive({
toupper(paste(c(input$main, input$desert), collapse = " & "))
})
)
output$myorder <- renderText(menuR())
}
shinyApp(ui, server)
Edit
I misunderstood the problem earlier. You can use eventReactive() which monitors a input and changes when the user input changes. I have also added a default value for when the action button is yet to be clicked by the user.
library(shiny)
ui <- fluidPage(
fluidRow(
column(2, radioButtons("main", label = "Main dish", choices = list("salad", "pasta"))),
column(2, radioButtons("desert", label = "Desert", choices = list("fruit", "cake"))),
column(8, actionButton("extra", "Louder!", style="background-color: #ffdb99"))
),
verbatimTextOutput("myorder")
)
server <- function(input, output, session) {
# Set a 'default' value for the output
default.menuR <- reactive({
paste(c(input$main, input$desert), collapse = " & ")
})
menuR <- eventReactive(input$extra, {
toupper(paste(c(input$main, input$desert), collapse = " & "))
})
# Initial state of the button is 0, which displays 'default' value
output$myorder <- renderText({
if (input$extra == 0) {
return(default.menuR())
}
menuR()
})
}
shinyApp(ui, server)
Hope this helps!

Answer 2

I have taken Vishesh's suggestion and made it work. It does not look much different than my original example, and still requires repeating several lines of code.
It works by over-writing the reactive object each time one of the widgets changes.
library(shiny)
ui <- fluidPage(
fluidRow(
column(2, radioButtons("main", label = "Main dish", choices = list("salad", "pasta"))),
column(2, radioButtons("dessert", label = "dessert", choices = list("fruit", "cake"))),
column(8, actionButton("extra", "Louder!", style="background-color: #ffdb99"))
),
verbatimTextOutput("myorder")
)
server <- function(input, output, session) {
menuR <- reactive({
paste(c(input$main, input$dessert), collapse = " & ")
})
# Render text when app loads
output$myorder <- renderText(menuR())
# Update reactive object and re-render text (button 'extra')
observeEvent(
input$extra,{
temp <- toupper(paste(c(input$main, input$dessert), collapse = " & "))
menuR <<- reactive(temp)
output$myorder <- renderText(menuR())
}
)
# Update reactive object and re-render text (button 'main' or 'dessert')
observeEvent(c(input$main, input$dessert),{
menuR <- reactive(paste(c(input$main, input$dessert), collapse = " & "))
output$myorder <- renderText(menuR())
})
}
shinyApp(ui, server)