如何从列表中显示一次项目，其中该项目在ruby中多次显示

I've written the code in my .html.erb file but am thinking it might more sense to write it in my controller? This code returns all the names. I'm trying to figure out how to fetch a tag name only once and if a user inputs a tag name that has already been used it does not show up again. I've written the code in my .html.erb file but