R Shiny stop for user input and display all plots - r

Question

I have a script which I want to add to my Shiny app, and the original script can be simplified to the following:
plot(c(1:3),c(2,4,6), main ="This is first plot I want displayed")
a <- menu(c(1:5), title="what would you like to change the first point to?")
plot(c(1:3),c(a,4,6), main ="This is second plot I want displayed")
b <- menu(c(1:5), title="what would you like to change the second point to?")
plot(c(1:3),c(a,b,6), main ="This is second plot I want displayed")
The above script plots the first plot, then waits for user input before plotting second, and waits again for user input before plotting third.
However, when I try to convert it to shiny app as seen below, it never updates the first or the second plot, and the things I've tried to make it stop for user input where shown have not worked.
I have tried using req() but it seems to stop the script entirely so the last things are not run at all, and you have to start the entire script over.
So, how can i make it display all plots in sequence, and how can I make the script stop and wait for input before continuing?
if(interactive()){
ui <- fluidPage(
actionButton("button","Click me"),
selectInput("input", "Input", c(1:10)),
textOutput("text"),
plotOutput("plot")
)
server <- function(input, output) {
a<-1
observeEvent(input$button, {
output$plot <- renderPlot(plot(c(1:3),c(2,4,6), main ="This is first plot I want displayed"))
output$text <- renderText("Please select a number to multiply the first point with")
#This is where I want the script to wait for user input
output$plot <- renderPlot(plot(c((1),(2),(3)),c((input$input),(a),(3)), main="This is plot the second plot"))
a<-a+1
#Here I want the script to wait for user input again
output$plot <- renderPlot(plot(c((1),(2),(3)),c((input$input),(a),(3)), main="This is plot the third plot"))
})
}
shinyApp(ui=ui, server=server)
}
The goal is that it updates the plots when they are rendered in the code, and that it waits for user input until script continues, instead of just keeping going.

Answer 1

Perhaps this is what you want.
req is used to only display when a variable is available. You need to create the second renderUI in the server since you cannot use req in the ui part.
if(interactive()){
ui <- fluidPage(
plotOutput("plot1"),
numericInput ("num1", "Please select a number to multiply the first point with", NA, 1, 10),
plotOutput("plot2"),
uiOutput("num2"),
plotOutput("plot3")
)
server <- function(input, output) {
output$plot1 <- renderPlot(plot(c(1:3),c(2,4,6), main ="This is first plot I want displayed"))
output$plot2 <- renderPlot({
req(input$num1)
plot(c(1:3),c(2*(input$num1),4,(6)),
main="This is plot the second plot"
)
}
)
output$plot3 <- renderPlot({
req(input$num1, input$num2)
plot(c(1:3),c(2*(input$num1)+(input$num2),4,(6)),
main="This is plot the third plot"
)
}
)
output$num2 <- renderUI({
req(input$num1)
numericInput ("num2", "Please select a number to add to first point", NA, 1, 10)
})
}
shinyApp(ui=ui, server=server)
}

Answer 2

To be honest, I´m not 100% sure if I know what you expect, even after reading your text 5 times. I have a guess ;-).
Your pause function, which cause plots to render one step after another can be done with invalidateLater. This has to "live" inside a reactiveValue. I don´t know exactly who is the creator of this function, I saved it in my snippets (all glory to the unknown person).
To render a plot or run a script based on the input of a user, try to catch it by using an if statement.
Hope this helps :-).
library(shiny)
if(interactive()){
ui <- fluidPage(
selectInput("input", "Input", c(1:10)),
actionButton("apply", "Apply"),
textOutput("text"),
plotOutput("plot")
)
server <- function(input, output, session) {
rv <- reactiveValues(i = 0)
maxIter <- 10
observeEvent(input$apply, {
rv$i <- 0
observe({
isolate({
rv$i <- rv$i + 1
})
if (isolate(rv$i) < maxIter){
invalidateLater(2000, session)
}
})
})
output$plot <- renderPlot( {
if(rv$i > 0) {
if(input$input <= 4) {
plot(c((rv$i*1),(rv$i*2),(rv$i*3)),c((1),(2),(3)), main = sprintf("Input <= 4; Round %i", rv$i), type = "l")
} else {
plot(c((rv$i*1),(rv$i*5),(rv$i*4)),c((1),(2),(3)), main = sprintf("Input > 4; Round %i", rv$i), type = "l")
}
} else {
plot(c(1:3),c(2,4,6), main ="This is first plot")
}
})
}
shinyApp(ui=ui, server=server)
}