r shiny - How to display a variable number of numeric inputs - r

Question

I would like to display a variable number of inputs based on a numeric input "number of lines". As there can be potentially a large number of lines, I don't want to use a conditional panel for each line and would rather iterate with functions as below:
ui <- fluidPage(
lapply(1:3,function(iter1){
fluidRow(
column(2,
h4(paste0("line", iter1))
),
lapply(1:4,function(iter2){
column(2,
h4(paste0("Wind speed bin", iter2)),
column(6, numericInput(paste0("v", iter1,"bin",iter2,"min"),"Vmin",5)),
column(6, numericInput(paste0("v", iter1, "bin",iter2,"max"),"Vmax",6))
)
})
)
})
)
The code above allows to display 4 wind speed bins definitions per line j (numericInput: vjbin1min, vjbin1max, vjbin2min, vjbin2max, ...) on 3 lines.
Overview of sidebar layout
I would like now to define the number of bins [of lines] with a variable bin_nb [line_nb] as below:
lapply(1:bin_nb,function(iter1){...
lapply(1:line_nb,function(iter2){...
With two numeric inputs
numericInput("bin_nb","number of wind speed bins",value=4),
numericInput("line_nb","number of lines",value=3)
I have tried to get the value from server side
output$bin_nb <- renderText(input$bin_nb)
And use
lapply(1:textOutput("bin_nb"),function(iter1){...
Which is of course not working as a numeric value is requested. How could I define and use these two numeric variables bin_nb and line_nb?

Answer 1

Based on BigDataScientist's comment, here is the detailed solution:
ui <- fluidPage(
numericInput("line_nb","number of lines",value=3),
numericInput("bin_nb","number of wind speed bins",value=4),
uiOutput("input_panel")
)
And server side:
server <- function(input, output) {
output$input_panel <- renderUI({
lapply(1:input$line_nb,function(iter1){
fluidRow(
column(2,
h4(paste0("line", iter1))
),
lapply(1:input$bin_nb,function(iter2){
column(2,
h4(paste0("Wind speed bin", iter2)),
column(6, numericInput(paste0("v", iter1,"bin",iter2,"min"),"Vmin",5)),
column(6,numericInput(paste0("v", iter1, "bin",iter2,"max"),"Vmax",6))
)
})
)
})
})
}