RStudio Shiny actionButton ignored - shiny

Question

Is the input$goButton in server.R that is triggered by actionButton supposed to be within an if statement in RStudio Shiny? The example on the Shiny webpage shows:
library(shiny)
shinyUI(pageWithSidebar(
headerPanel("Click the button"),
sidebarPanel(
sliderInput("obs", "Number of observations:",
min = 0, max = 1000, value = 500),
actionButton("goButton", "Go!")
),
mainPanel(
plotOutput("distPlot")
)
))
and
library(shiny)
shinyServer(function(input, output, message) {
output$distPlot <- renderPlot({
# Take a dependency on input$goButton
input$goButton
# Use isolate() to avoid dependency on input$obs
dist <- isolate(rnorm(input$obs))
hist(dist, main=isolate(paste(system(paste("echo", dist[1],"> /tmp/1 && md5sum /tmp/1"),intern=TRUE),collapse='')))
})
})
I have a slightly more complicated routine with more statements that the example above, and the event takes place event before the user clicks on the Go button. It makes me think input$goButton is ignored when one of the statements in the reactive is an R system() call.
Shiny Server v1.1.0.10000
Node.js v0.10.21
packageVersion: 0.10.0
Any ideas?

Answer 1

I this what you want? Whenever the button is pressed it will increase the count + 1 (starting with 0), hence there's and if statement with return() "nothing" if it hasn't been pressed
rm(list = ls())
library(shiny)
runApp(list(ui = pageWithSidebar(
headerPanel("Click the button"),
sidebarPanel(
sliderInput("obs", "Number of observations:",min = 0, max = 1000, value = 500),
actionButton("goButton", "Go!")
),
mainPanel(plotOutput("distPlot"))),
server = function(input, output,session) {
my_data <- reactive({
if(input$goButton == 0)
{
return()
}
isolate({
input$goButton
dist <- isolate(rnorm(input$obs))
hist(dist, main=isolate(paste(system(paste("echo", dist[1],"> /tmp/1 && md5sum /tmp/1"),intern=TRUE),collapse='')))
})
})
output$distPlot <- renderPlot({my_data()
})
}
)
)