inject.rb

#БЫЛО
tier1.uniq_by!(&:id).sort_by! { rand }.sort_by! {|x| x.avatar_file_name.blank? ? 1 : 0} +
        tier2.uniq_by!(&:id).sort_by! { rand }.sort_by! {|x| x.avatar_file_name.blank? ? 1 : 0} +
        tier3.uniq_by!(&:id).sort_by! { rand }.sort_by! {|x| x.avatar_file_name.blank? ? 1 : 0} +
        (instructors - tier1 - tier2 - tier3).uniq_by!(&:id).sort_by! { rand }.sort_by! {|x| x.avatar_file_name.blank? ? 1 : 0}


#СТАЛО
instructors = [tier1,tier2,tier3].inject {|result, x| result + tier_filter(x) } +
              tier_filter(instructors - tier1 - tier2 - tier3)

private 
def tier_filter(tier)
	tier.uniq_by!(&:id).sort_by! { rand }.sort_by! {|x| x.avatar_file_name.blank? ? 1 : 0}
end