Change error message with Shiny app

Question

Simply, I have a Shiny app, where users can select various combinations of values in a data set and produces a graph. However for some of those combinations there is no data and Shiny produces an error message:

Error: 'from' must be length 1

How can I replace this error message with a more informative message, like:

Sorry, there is no data for you requested combination. Please change your input selections

Thanks.

Answer 1

You can do this using the validate and need functions. The code would look something like this:

output$MyPlot<-renderPlot({
  validate(
     need(MyData(), "Sorry, there is no data for you requested combination. 
                      Please change your input selections"
     )
   )
   ...code for making plot...
})

If the MyData() part does not exist due to giving an error, than the message will display, otherwise the plot will. Check ?validate for all the details.