Shiny updating whilst function is running? - r

Question

On clicking "Start Ramp", I am expecting the display to update with the new counter value every time add.to.counter(ticks_per_second) is run in the for loop, but the update only happens at the end of the for loop. Is this because the main ramp function is still executing? How could I make this update such that it updates on each change of the counter value - whilst that main function is still running?
library(shiny)
library(shinyjs)
ui <- fluidPage(
useShinyjs(),
sidebarLayout(
sidebarPanel(
actionButton("start", "Start Ramp")
),
mainPanel(
tags$b("Simple counter using reactiveValues() - An example"),
br(),
actionButton("add1", "+ 1"),
actionButton("sub1", "- 1"),
actionButton("reset", "set to 0"),
br(),
textOutput("count")
)
))
server <- function(input, output, session) {
counter <- reactiveValues(countervalue = 0) # Defining & initializing the reactiveValues object
add.to.counter <- function(val) {
counter$countervalue <<- counter$countervalue + val
}
ramp <- function(length_of_ramp, ticks_per_second) {
# length of ramp in seconds
# ticks: divide each second into this number of ticks
ticks <- length_of_ramp*ticks_per_second
for (n in 1:ticks) {
shinyjs::delay(ticks_per_second*1000, add.to.counter(ticks_per_second))
}
}
observeEvent(input$start, { ramp(length_of_ramp = 10, ticks_per_second = 1) }
)
observeEvent(input$add1, {
counter$countervalue <- counter$countervalue + 1 # if the add button is clicked, increment the value by 1 and update it
})
observeEvent(input$sub1, {
counter$countervalue <- counter$countervalue - 1 # if the sub button is clicked, decrement the value by 1 and update it
})
observeEvent(input$reset, {
counter$countervalue <- 0 # if the reset button is clicked, set the counter value to zero
})
output$count <- renderText({
paste("Counter Value is ", counter$countervalue) # print the latest value stored in the reactiveValues object
})
}
# Run the application
shinyApp(ui = ui, server = server)

Answer 1

Your use of Sys.sleep() in
library(shiny)
ui <- fluidPage(
sidebarLayout(
sidebarPanel(
actionButton("start", "Start Ramp")
),
mainPanel(
tags$b("Simple counter using reactiveValues() - An example"),
br(),
actionButton("add1", "+ 1"),
actionButton("sub1", "- 1"),
actionButton("reset", "set to 0"),
br(),
textOutput("count")
)
))
server <- function(input, output, session) {
add.to.counter <- function(val) {
counter$countervalue <<- counter$countervalue + val
}
ramp <- function(length_of_ramp, ticks_per_second) {
# length of ramp in seconds
# ticks: divide each second into this number of ticks
ticks <- length_of_ramp*ticks_per_second
for (n in 1:ticks) {
add.to.counter(ticks_per_second)
# Sys.sleep(1/ticks_per_second)
}
}
observeEvent(input$start, { ramp(length_of_ramp = 10, ticks_per_second = 1) }
)
counter <- reactiveValues(countervalue = 0) # Defining & initializing the reactiveValues object
observeEvent(input$add1, {
counter$countervalue <- counter$countervalue + 1 # if the add button is clicked, increment the value by 1 and update it
})
observeEvent(input$sub1, {
counter$countervalue <- counter$countervalue - 1 # if the sub button is clicked, decrement the value by 1 and update it
})
observeEvent(input$reset, {
counter$countervalue <- 0 # if the reset button is clicked, set the counter value to zero
})
output$count <- renderText({
paste("Counter Value is ", counter$countervalue) # print the latest value stored in the reactiveValues object
})
}
# Run the application
shinyApp(ui = ui, server = server)

Answer 2

I think the problem is that shinyjs::delay() only delays once even when called within a for loop. I do not know how to make shinyjs::delay() delay each iteration of the for loop. In fact, I suspect that this is not possible, given that shinyjs::delay() only works in interactive sessions or context, whereas the for loop itself is not an interactive or reactive context.
To attain what you want, I've had to have a bit of a rethink on the server code. I've made use of invalidateLater, isolate, and reactiveValue to get the text output to update every second and to calculate the counter every second such that each second, the counter is updated in the text output. Since, this will run forever unless some values are changed, I've used if statements to conditionally print the text output.
Full code below:
library(shiny)
ui <- fluidPage(
useShinyjs(),
sidebarLayout(
sidebarPanel(
actionButton("start", "Start Ramp")
),
mainPanel(
tags$b("Simple counter using reactiveValues() - An example"),
br(),
actionButton("add1", "+ 1"),
actionButton("sub1", "- 1"),
actionButton("reset", "set to 0"),
br(),
uiOutput("count")
)
))
server <- function(input, output, session) {
length_of_ramp = 10; ticks_per_second = 1
ticks <- length_of_ramp*ticks_per_second
counter <- reactiveValues(countervalue = 0, forLoop = ticks, loopCount = Inf, finalCount = 0)
observeEvent(input$start, {
counter$loopCount <- -1
})
observe({
invalidateLater(1000)
counter$loopCount <- isolate(counter$loopCount) + 1
if(counter$loopCount == ticks){counter$finalCount <- counter$loopCount}
print(counter$finalCount)
})
observeEvent(input$add1, {
counter$countervalue <- counter$countervalue + 1 # if the add button is clicked, increment the value by 1 and update it
})
observeEvent(input$sub1, {
counter$countervalue <- counter$countervalue - 1 # if the sub button is clicked, decrement the value by 1 and update it
})
observeEvent(input$reset, {
counter$countervalue <- 0 # if the reset button is clicked, set the counter value to zero
})
output$count <- renderUI({
invalidateLater(millis = 1000, session)
if(counter$loopCount < ticks){
counter$countervalue <- isolate(counter$countervalue) + ticks_per_second
paste("Counter Value is ", isolate(counter$countervalue))
}else if (counter$loopCount == Inf || counter$loopCount == 0 || counter$finalCount == ticks) {
paste("Counter Value is ", isolate(counter$countervalue))
}
})
}
shinyApp(ui, server)