Hello, I have a general question about graphs containing a 'by' set. I am attempting to show how unionization rates have declined by education level over the years. I have attached an image of my two way line graph, I want every level of education to contain an x-axis with the relevant years. Is there a method to make this happen? I cannot find anything in the help section pertaining to this topic, any help is appreciated. Thanks!

Relevant code:
collapse (mean) Union , by(Schooling survyear)
twoway line Union survyear, by(Schooling)


Array