Reactive Loop in R Shiny - r

Question

I've been stuck on this problem for hours. I tried to create a simpler version of my actual use case to see if I can debug the problem but still having trouble.
My shiny app is below. It takes an input from user, runs it through some calculations until it meets a threshold, then collects the value in a list. It does this for several iterations (10 here in the example), then plots a histogram of these values.
The specific error I'm getting says
Warning: Error in : evaluation nested too deeply: infinite recursion / options(expressions=)?
I think that my error is related to the way I'm using x.new, but I can't figure out how to code it differently.
# install.packages('shiny')
library(shiny)
ui <- fluidPage(
headerPanel('Title Here'),
sidebarPanel(
numericInput('x.qty', 'Pick a number', 3, 1, 10)),
mainPanel(plotOutput('valueplot'))
)
server <- function(input, output, session) {
results <- reactive({
x.list <- list()
for (i in 1:10){
x.new <- reactive({input$x.qty * sample(1:10, 1)})
repeat{
if (x.new() > 20){
x.list <- c(x.list, x.new())
results <- x.list
break
} # end if loop
x.new <- reactive({x.new() * sample(1:10, 1)})
} # end repeat
} # end for loop
results
})
output$valueplot <- renderPlot({hist(as.numeric(results()))})
}
shinyApp(ui = ui, server = server)

Answer 1

I would suggest to modify your server function in the following way:
server <- function(input, output, session) {
results <- reactive({
x.list <- list()
for (i in 1:10){
x.new <- input$x.qty * sample(1:10, 1)
repeat{
if (x.new > 20){
x.list <- c(x.list, x.new)
results <- x.list
break
} # end if loop
x.new <- x.new * sample(1:10, 1)
} # end repeat
} # end for loop
results
})
output$valueplot <- renderPlot({hist(as.numeric(results()))})
}
This way you avoid the infinite recursion provoked by
x.new <- reactive({x.new() * sample(1:10, 1)})

Answer 2

Does this work as you want? Each for loop iteration, x.new is calculated using x.qty then in the repeat loop x.new recursively multiplies itself by a random number until it is greater than 20.
library(shiny)
ui <- fluidPage(headerPanel('Title Here'),
sidebarPanel(numericInput('x.qty', 'Pick a number', 3, 1, 10)),
mainPanel(plotOutput('valueplot')))
server <- function(input, output, session) {
x.new <- function(x) {
x * sample(1:10, 1)
}
results <- reactive({
x.list <- list()
for (i in 1:10) {
x.new_draw <- x.new(input$x.qty)
repeat {
if (x.new_draw > 20) {
x.list <- c(x.list, x.new_draw)
break
} # end if loop
x.new_draw <- x.new(x.new_draw)
} # end repeat
} # end for loop
x.list
})
output$valueplot <- renderPlot({
hist(as.numeric(results()))
})
}
shinyApp(ui = ui, server = server)