Yes you call each on an array. If you have any doubts you can simply check the ruby (or rails) doc: http://www.ruby-doc.org/core-2.1.1/Array.html
P.s. I would write tests for every step if I were you. This way you can see if every part is returning the right result. Without tests you could use binding.pry to check for unexpected outcomes. In your case I wonder if @concert.artist.upcomingEvents returns anything but an empty array.