Handling errors (including validate() and req())

Are you getting an error message in red on your screen? Are you or your user able to understand that message? The answers to such questions can be validation errors using validate() and req().

Validate

This is designed to lead the user through the UI of the Shiny app. Imagine that we have a situation where we need to plot a graph based on some values of a list box and it throws up a red message. This looks stressful to the user. We need to provide a precautionary message to make sure the reader enters a valid input. validate is a way of checking the input and providing a message, using need. In the following code, we can see that validate is checking for a phone number. If the...