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An example of doing prolonged, iterative computation in Shiny.
library(shiny)
shinyServer(function(input, output, session) {
# The number of iterations to perform
maxIter <- 50
# Track the start and elapsed time
startTime <- Sys.time()
output$elapsed <- renderText({
vals$x
round(Sys.time() - startTime)
})
# Create a reactiveValues object where we can track some extra elements
# reactively.
vals <- reactiveValues(x = 0, counter = 0)
# Update the percentage complete
output$counter <- renderText({
paste0(round(vals$counter/maxIter * 100, 1), "%")
})
# Show the value of x
output$x <- renderText({
round(vals$x,2)
})
# Do the actual computation here.
observe({
isolate({
# This is where we do the expensive computing
sum <- 0
for (i in 1:100000){
sum <- sum + rnorm(1)
}
vals$x <- vals$x + sum
# Increment the counter
vals$counter <- vals$counter + 1
})
# If we're not done yet, then schedule this block to execute again ASAP.
# Note that we can be interrupted by other reactive updates to, for
# instance, update a text output.
if (isolate(vals$counter) < maxIter){
invalidateLater(0, session)
}
})
})
library(shiny)
shinyUI(pageWithSidebar(
# Application title
headerPanel("New Application"),
sidebarPanel(
"Progress: ",
textOutput("counter"),
hr(),
"Elapsed Time (seconds):",
textOutput("elapsed")
),
mainPanel(
textOutput("x")
)
))
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