Value of dynamic UI input lost every time main input change - shiny

Question

library(shiny)
ui <- shiny::fluidPage(
shiny::titlePanel("Dynamic UI"),
shiny::sidebarLayout(
shiny::sidebarPanel(width = 2,
shiny::numericInput("num", "Number of input", value=1, min=1, max=7),
htmltools::hr(style = "border-top: 5px dashed skyblue"),
shiny::uiOutput("out")
),
shiny::mainPanel()
)
)
server <- function(input, output, session) {
output$out <- shiny::renderUI({
lapply(1:input$num, function(i) {
htmltools::div(
htmltools::tags$h4(paste0("Input group: ",i)),
shiny::numericInput(paste0("size", i),
label = "size",
value = 3, min = 1, max = 8
),
shiny::numericInput(paste0("inc", i),
label = "incidence",
value = 1, min = 1, max = 8
),
htmltools::hr(style = "border-top: 2px dashed skyblue")
)
})
})
}
shiny::shinyApp(ui, server)
I created an example of app that dynamically create multiple numeric input depending on other input(Number of input here).
Now when Number of input value changes, all the input value that are dynamically created is reset.
I know that because server side creating these input every time Number of input changes.
But, are there any way/trick so dynamic input value will remain unchanged when user change the Number of input?

Answer 1

Use react<-reactiveValues() to have saved values.
Use observeEvent(input$num, {}) to save input values in react values.
library(shiny)
ui <- shiny::fluidPage(
shiny::titlePanel("Dynamic UI"),
shiny::sidebarLayout(
shiny::sidebarPanel(width = 2,
shiny::numericInput("num", "Number of input", value=1, min=1, max=7),
htmltools::hr(style = "border-top: 5px dashed skyblue"),
shiny::uiOutput("out")
),
shiny::mainPanel()
)
)
server <- function(input, output, session) {
react <- reactiveValues(
S=list(),
I=list()
)
output$out <- shiny::renderUI({
lapply(1:input$num, function(i) {
input_size<- isolate(input[[paste0("size", i)]])
input_inc <- isolate(input[[paste0("inc", i)]])
if (is.null(input_size)){
input_size<-3
}
if (is.null(input_inc)){
input_inc<-1
}
htmltools::div(
htmltools::tags$h4(paste0("Input group: ",i)),
shiny::numericInput(paste0("size", i),
label = "size",
value = input_size , min = 1, max = 8
),
shiny::numericInput(paste0("inc", i),
label = "incidence",
value = input_inc, min = 1, max = 8
),
htmltools::hr(style = "border-top: 2px dashed skyblue")
)
})
})
observeEvent(input$num, {
i <- input$num
react$S[i]<- input[[paste0("size", i)]]
react$I[i]<- input[[paste0("inc", i)]]
},ignoreNULL = TRUE, ignoreInit = TRUE
)
}
shiny::shinyApp(ui, server)