Before the user has selected any choice from a field (in this case a dimension), all choices are selected. I'd like to make it so that if the user hasn't selected any choices, it defaults to a predefined choice.
This is what I've tried in the field equation editor of the graph.
if(match([sem type], 'Vietnam'), [Term Code]),
if nothing is selected, set it to 'Vietnam', otherwise, use what the user has selected.
It does set it initially to 'Vietnam', but when I change it to another choice, it doesn't work.