Using Shiny to create a comma delimited string list - shiny

Question

How do you handle it in Shiny when you need to append a value to an already existing output?
To simplify my problem:
I want to create a comma separated code list in a single variable ie:
02,04,05,11,31
and display the list as I go creating it. I validate the codes as I go, that is not the problem.
I currently have a text input widget to enter my codes.
I want to append to the list the value in the text input field, every time I press an action button.
Are there any examples of how to do this?
Shiny does not like it when I try to use an output object and append something to it.

Answer 1

You can use Paste to do that. Im sure there are many other ways to do it, look into this example here reactivePoll and reactiveFileReader in the gallery section. Below are a sample code where I simply print out the Sys.time() and append it to the last entry.
Here are two examples:
Example 1 without the button
library(shiny)
runApp(list(ui = fluidRow(wellPanel(verbatimTextOutput("my_text"))),
server = function(input, output, session) {
autoInvalidate <- reactiveTimer(1000,session)
my_file <- as.character(Sys.time())
output$my_text <- renderText({
autoInvalidate()
my_file <<- paste(my_file,as.character(Sys.time()), sep=",")
})
})
)
Example 2 with the ActionButton
library(shiny)
runApp(list(ui = fluidRow(actionButton("push","Append"),wellPanel(verbatimTextOutput("my_text"))),
server = function(input, output, session) {
my_file <- as.character(Sys.time())
output$my_text <- renderText({
if(input$push==0)
{
return(my_file)
}
isolate({
input$push
my_file <<- paste(my_file,as.character(Sys.time()), sep=",")
})
})
})
)