Adding a moving vline in a Shiny Application (based on user input) - r

Question

I have the following shiny application:
library(shinydashboard)
library(ggplot2)
library(dplyr)
UI <- dashboardPage(
dashboardHeader(title = ""),
dashboardSidebar(
),
dashboardBody(
mainPanel(
actionButton("goButton", "Go!"),
plotOutput("plot_timeseries")
)
)
)
Server <- function(input, output) {
output$plot_timeseries <- renderPlot({
ggplot(mtcars, aes(mpg, disp)) + geom_point()+
scale_x_continuous(limits = c(0,35)) +
geom_vline(xintercept = 1)
})
}
shinyApp(ui = UI, server = Server)
As you'll see I have a vline now at x = 1. However what I would like to achieve it that when I press the "go" button a counter should be initiated (adding 1 with every second). So 5 seconds after pressing the go button the variable should 6 and the vline value should be 6.
Any thoughts on how I can get this working in the example above?

Answer 1

Here is a possible solution, which uses two reactiveVal's; one to keep track of whether the counter should increment, and one with the current value of the counter.
Hope this helps!
library(shiny)
library(shinydashboard)
library(ggplot2)
library(dplyr)
UI <- dashboardPage(
dashboardHeader(title = ""),
dashboardSidebar(
),
dashboardBody(
mainPanel(
actionButton("goButton", "Go!"),
plotOutput("plot_timeseries")
)
)
)
Server <- function(input, output, session) {
counter <- reactiveVal(1)
action <- reactiveVal(FALSE)
# When goButton is clicked, set action() from FALSE to TRUE or the other way around.
observeEvent(input$goButton,
{
action(!action())
})
# Add an oberserver that invalidates every second, and increments the counter if action()==TRUE
observe({ invalidateLater(1000, session)
isolate({
if(action())
{
# Add 1 to our counter
counter(counter() + 1)
}
})
})
output$plot_timeseries <- renderPlot({
ggplot(mtcars, aes(mpg, disp)) + geom_point()+
scale_x_continuous(limits = c(0,35)) +
geom_vline(xintercept = counter())
})
}
shinyApp(ui = UI, server = Server)