persistent data storage of user input in R Shiny

app.R

library(shiny)
library(shinyWidgets)
library(tidyverse)

# read persistent data or create a new file if it does not exist yet
if ("favs.csv" %in% list.files()) {
  favs <- read_file("favs.csv") %>% 
    strsplit(", ") %>% 
    .[[1]] %>% 
    as.numeric() %>% 
    .[-1]
} else {
  favs <- 99
  paste(favs, collapse = ", ") %>% write_file("favs.csv")
  favs <- favs[-1]
}

ui <- fluidPage(
  radioGroupButtons(
    inputId = "fav_number", 
    label = "What's your favorite number?", 
    choices = 1:9
    
  ),
  
  circleButton("button_go", "Go!"),
  
  plotOutput("plot")
)

server <- function(input, output, session) {
  
  rfavs <- reactiveVal(favs)
  
  observeEvent(input$button_go, {
    req(input$fav_number)
    
    write_file(paste0(", ", input$fav_number), "favs.csv", append = T)
    
    isolate({
      rfavs(c(rfavs(), as.integer(input$fav_number)))
    })
  })
  
  output$plot <- renderPlot({
    hist(rfavs(), breaks = 1:9)
  })
  
}

shinyApp(ui, server)