How can I ensure the observation is called before renderPlot in my shiny app
I have a brilliant app with two selectInputs (L1 and L2) with an observer that updates L2 based on L1 selection using updateSelectInput. I also have renderPlot output which depends on both options. The problem I'm running into is that whenever I change L1, renderPlot is called twice, once with the old L2 value and once with the new value (set in updateSelectInput). My code is below:
ui.R
shinyUI(
fluidPage(
titlePanel("Nested Selects Problem"),
sidebarLayout(
sidebarPanel(
selectInput(
"L1",
label = "L1",
choices = c("red", "blue")
),
selectInput(
"L2",
label = "L2",
choices = ""
)
),
mainPanel(
plotOutput("plot")
)
)
)
)
server.R
shinyServer(
function(input,output,session) {
observe({
if (input$L1 == "red") {
choices <- c(1000000,2000000,3000000)
}
else {
choices <- c(10,20,30)
}
updateSelectInput(session,"L2",choices=choices,selected=choices[1])
})
output$plot <- renderPlot({
if (input$L2 != "") {
plot(runif(as.numeric(input$L2)),col=input$L1)
}
})
})
How can I avoid the first call to renderPlot? It seems to me that if I could arrange for observation () to be called before the first renderPlot, I would get the desired effect.
Thank you for your help.
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You can use isolate
to call input$L1
inside renderPlot
. Thus, changes should propagate from your call updateSelectInput
only when you change input$L1
:
library(shiny)
runApp(list(
ui = fluidPage(
titlePanel("Nested Selects Problem"),
sidebarLayout(
sidebarPanel(
selectInput("L1",label = "L1",choices = c("red", "blue")),
selectInput("L2",label = "L2",choices = "")
),
mainPanel(
plotOutput("plot")
)
)
)
, server = function(input,output,session) {
observe({
if (input$L1 == "red") {
choices <- c(100,200,300)
}
else {
choices <- c(10,20,30)
}
updateSelectInput(session,"L2",choices=choices,selected=choices[1])
})
output$plot <- renderPlot({
if (input$L2 != "") {
plot(runif(as.numeric(input$L2)),col=isolate(input$L1))
}
})
})
)
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Well, how about:
shinyServer(
function(input,output,session) {
L1_selected <- reactiveValues(triggered=-1)
observe({
if (input$L1 == "red") {
choices <- c(10, 100,200,300)
}
else {
choices <- c(10,20,30)
}
old_L2 <- isolate(input$L2)
updateSelectInput(session,"L2",choices=choices,selected=choices[1])
isolate(L1_selected$triggered <- L1_selected$triggered + as.numeric(old_L2 != choices[1]))
})
output$plot <- renderPlot({
if (input$L2 != "") {
if (isolate(L1_selected$triggered)) {
isolate(L1_selected$triggered <- L1_selected$triggered - 1)
return()
} else {
plot(runif(as.numeric(input$L2)),col=input$L1)
}
}
})
})
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