Read and overwrite data at each click of an actionButton - r

Question

I am trying to build a shiny app that reads a data frame and at every press of an actionButton returns the value of a specific column, one row at a time until all rows of the data frame have been read. The structure of the dataset is 3 columns, one for IDs, one for a characteristic and an indicator variable for the already read IDs (0/1). Every time the user presses the actionButton, the app reads one row of the dataset, starting from row 1, returns the value of a second variable in that row and changes the value of the third variable to 1. The tricky part for me is that I want to save the "used" ids, in order to continue the reading from the last used id after restarting the app. I have tried loading and saving the data at every step and using reactiveValues, but this does not seem to work well for me - probably I don't know how to use them correctly. I am very new in shiny, so any feedback is more than welcome.
An example of the code I have been using:
project.path <- getwd()
dat <- data.frame(id = c(1:20), gender = sample(c("male", "female"), 20, replace = TRUE), used = 0)
write.csv2(dat, file.path(project.path, "data.csv"), row.names = F)
saveData <- function(x) {
write.csv2(x, file = file.path(project.path, "data.csv"),
row.names = FALSE)
}
loadData <- function() {
dat <- read.csv2(file.path(project.path, "data.csv"))
return(dat)
}
# UI
ui <- fluidPage(
# Application title
titlePanel("Tittle"),
sidebarLayout(
sidebarPanel(
actionButton("counter", "Start")
),
mainPanel(
textOutput("result")
)
)
)
# SERVER
server <- function(input, output, session) {
last <- reactive({
d <- loadData()
last <- min(d$id[d$used == 0]) -1
})
cur <- reactive({
if(last() == 0){
cur <- input$counter
}else{
cur <- last() + input$counter
}
})
# Calculate Result
ResultText <- reactive({
d <-loadData()
if (input$counter == 0 & last() == 0){
paste0("No IDs have been used. Press button to start.")
}else{
if(input$counter > 0 & last() == 0){
d$used[cur()] <- 1
paste0("ID ", cur(), " is a ", as.character(d$gender[cur()]))
}else{
if(input$counter == 0 & last() > 0){
paste0("The last ID was ", d$id[last()], " (", as.character(d$gender[last()]), ") Press the button to continue reading the list.")
}else{
d$used[cur()] <- 1
paste0("ID ", cur(), " is a ", as.character(d$gender[cur()]))
}
}
}
})
output$result <- renderText({
ResultText()
})
observe({
d <- loadData()
if (input$counter > 0 & last() == 0){
cur <- input$counter
d$used[cur] <- 1
saveData(d)
}else{
if(input$counter > 0 & last() > 0){
d$used[cur()] <- 1
saveData(d)
}
}
})
}
# Run
shinyApp(ui = ui, server = server)