Method to exclude duplicate values in repeat fields

Idea created by beasleyc on Jun 19, 2017

    I have a Select_One field in a Repeat group and I would like to be able to prevent users from selecting the same answer twice in different instances of the Repeat. Specifically, it is a plant species list, and once a user has entered details (area covered) for a particular plant species, accidentally entering it twice would mess up the calculated results (total plant coverage). There may be multiple ways to achieve this, but I would imagine the easiest might be an expression in the Constraint column that either requires a Unique response or excludes a Duplicate response in that particular field. Another option might be to create a type of Select list that removes answers as they are selected, but the Constraint option would likely be more versatile, as it could by applied to Text and other types fields as well.