ShinyApp - reactive inferno - shiny

Question

I have two input variables, and changing one will cause the change of the other one.
Further to that, if the value of input is outside limits it should default to min (if below) or max (if above) value.
All works fine as long as up and down arrows are being used.
The moment I am typing value 1 in Input1 it goes crazy.
Same if I am deleting Input2, even before I am typing anything...
I am aware that it must have something to do with reactive values, but can not fix it...
Any suggestion will be very much appreciated!
library(shiny)
ui <- fluidPage(
fluidRow(
uiOutput("Input1"),
numericInput("Input2", "Input 2",
min = 50, max = 150,
value = 100, step = 1)),
tableOutput("result")
)
#########################################################
server <- function(input, output, session) {
global <- reactiveValues(numVal = 10, numMin = 5, numMax = 15)
numVal <- reactive({
if(!is.null(input$Input1)){
if(input$Input1 < global$numMin) return(global$numMin)
if(input$Input1 > global$numMax) return(global$numMax)
return(input$Input1)
}else{
return(global$numVal)
}
})
output$Input1 <- renderUI(numericInput("Input1", "Input 1",
min = global$numMin, max = global$numMax,
value = numVal(), step = 0.1))
# when Input1 change, update Input2
observeEvent(input$Input1, {
updateNumericInput(session = session,
"Input2",
value = format(round(input$Input1*10, 0), nsmall = 0))
})
# when Input2 change, update Input1
observeEvent(input$Input2, {
updateNumericInput(session = session,
"Input1",
value = format(round(input$Input2*0.1, 1), nsmall = 1))
})
inputdata <- reactive({
data <- data.frame(Coef = as.numeric(input$Input1))
data
})
output$result <- renderTable({
data = inputdata()
resultTable = as.character(round((data$Coef + 10)*100, digits=2))
resultTable
})
}
#########################################################
shinyApp(ui, server)

Answer 1

You are on the brink of getting into a race condition:
Input 1 changes Input 2 changes Input 1 changes Input 2...
So foremost you should reconsider your design. You can use debounce / throttle to avoid some of the race consition by telling Shiny not too fire too quickly and as the updates are bijective you may achieve what you want, but I would really think about your design b/c these circle dependencies are almost never a good idea.
Having said that here is a solution which behaves better (N.B. I removed the dynamic rendering of the second input element as it has nothing to do wiht the problem at hand). It is not perfect, b/c you will eventually end up in a racing condition, but you can soften this situation by playing w/ the debouncing factors.
library(shiny)
ui <- fluidPage(
fluidRow(
numericInput("Input1", "Input 1",
min = 5, max = 15, value = 10, step = .1),
numericInput("Input2", "Input 2",
min = 50, max = 150,
value = 100, step = 1)),
tableOutput("result")
)
server <- function(input, output, session) {
## debounce both input, i.e. they are firing onyl if no change within 1sec happens
## c.f. ?debounce
getI1 <- reactive(input$Input1) %>%
debounce(1000)
getI2 <- reactive(input$Input2) %>%
debounce(1000)
observeEvent(input$Input1, {
updateNumericInput(session = session,
"Input2",
value = format(round(getI1() * 10, 0), nsmall = 0))
})
observeEvent(input$Input2, {
updateNumericInput(session = session,
"Input1",
value = format(round(getI2() * 0.1, 1), nsmall = 1))
})
inputdata <- reactive({
data <- data.frame(Coef = as.numeric(input$Input1))
data
})
output$result <- renderTable({
data = inputdata()
resultTable = as.character(round((data$Coef + 10)*100, digits=2))
resultTable
})
}
shinyApp(ui, server)