Hi Greg,
Isolate may not solve the problem. For the following code. It runs only
1-2 times and stopped without isolate. If we update the slider with same
value, it will not send a new message.
library("shiny")
ui <- fluidPage(
titlePanel("Slider Test"),
sidebarLayout(
sidebarPanel(
min=2, max=10, value=10),
sliderInput("sliderB", "B:",
min = 1, max = 5, value = 5)
),
mainPanel(
plotOutput("plot")
)
)
)
server <- function(input, output, clientData, session) {
observeEvent(input$sliderA,{updateSliderInput(session, "sliderB",
value as.integer(input$sliderA/2))})
observeEvent(input$sliderB,{updateSliderInput(session, "sliderA",
value isolate(input$sliderB*2))})
}
shinyApp(server = server, ui = ui)
For example:
set B: 4 -> update A: 8 -> update B: 8 (same, no message, end)
changing of A is tricky
If original A is 10, B is 5.
set A: 9 -> update B: 4 (not same, continue) -> update A: 8 (not same,
continue) -> update B: 4 (same, no message, end)
If original A is 8, B is 4.
set A:9 - > update B: 4(same, no message, end)
isolate doesn't work in this case.
Instead, use the following code:
library("shiny")
ui <- fluidPage(
titlePanel("Slider Test"),
sidebarLayout(
sidebarPanel(
min=2, max=10, value=10),
sliderInput("sliderB", "B:",
min = 1, max = 5, value = 5)
),
mainPanel(
plotOutput("plot")
)
)
)
server <- function(input, output, clientData, session) {
server <- function(input, output, clientData, session) {
ignoreNext <- ""
observeEvent(input$sliderA,{
if (ignoreNext == "A") {
ignoreNext <<- ""
}
else{
valB <- as.integer(input$sliderA/2)
if(valB != input$sliderB){
ignoreNext <<- "B"
updateSliderInput(session, "sliderB", value = valB)
}
}
})
observeEvent(input$sliderB,{
if (ignoreNext == "B") {
ignoreNext <<- ""
}
else{
valA <- as.integer(input$sliderA*2)
if(valA != input$sliderA){
ignoreNext <<- "A"
updateSliderInput(session, "sliderA", value = valA)
}
}
})
}
shinyApp(server = server, ui = ui)
2016-03-08 18:00 GMT-05:00 Greg Snow <538280 at gmail.com>:
> You need to use `isolate` on one of the assignments so that it does
> not register as an update. Here are a few lines of code from the
> server.R file for an example that I use that has a slider for r
> (correlation) and another slider for r^2 and whenever one is changed,
> I want the other to update:
>
> observe({
> updateSliderInput(session, 'r',
> value=isolate(ifelse(input$r<0,-1,1))*sqrt(input$r2))
> })
>
> observe({
> updateSliderInput(session, 'r2', value=input$r^2)
> })
>
>
> I did end up in a loop once when I happened to choose just the wrong
> value and the rounding caused a jumping back and forth, but all the
> other times this has worked perfectly without the endless loop.
>
>
> On Tue, Mar 8, 2016 at 12:35 PM, Michael Peng
> <michael.gang.peng at gmail.com> wrote:
> > Hi,
> >
> > I added two sliderInput into the app with package "shiny":
sliderA and
> > sliderB. The values in the two sliders are correlated. If I change
> sliderA,
> > I used updateSliderInput to update the value in sliderB. And also If I
> > change sliderB, I used updateSliderInput to update the value in
slideA.
> >
> > The problem is it is an endless loop. How can I use updateSliderInput
> > without sending message to update the other slider.
> >
> > Thank.
> >
> > [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
>
>
>
> --
> Gregory (Greg) L. Snow Ph.D.
> 538280 at gmail.com
>
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