refactor a ruby method

Question

I seem to be writing quite a few methods with the following pattern and it seems like there should be a better way. Is there a one-liner for this or a better practice?

def combine_roster(roster)
  rstr = []
  roster.each do |r|
    rstr << r.user
  end
  rstr
end

Answer 1

Yes, you can use the map command. Here is the short hand version for what you are trying to do:

roster.map(&:user) # if roster = [r1, r2, r3] then the output will be [r1.user, r2.user, r3.user]

You can read more about the map function in the Ruby Array API: http://ruby-doc.org/core-2.0.0/Array.html#method-i-map