.inject(:+)

2.3.0 :001 > class SummaryRow
2.3.0 :002?>   attr_accessor :user_id, :name
2.3.0 :003?>   def +(row)
2.3.0 :004?>     newRow = SummaryRow.new
2.3.0 :005?>     newRow.user_id = @user_id
2.3.0 :006?>     newRow.name = @name
2.3.0 :007?>     return newRow
2.3.0 :008?>     end
2.3.0 :009?>   end
 => :+ 
2.3.0 :010 > summary1 = SummaryRow.new
 => #<SummaryRow:0x00000001b90068> 
2.3.0 :011 > summary1.user_id = 1; summary1.name = 'first'
 => "first" 
2.3.0 :012 > puts summary1.inspect
#<SummaryRow:0x00000001b90068 @user_id=1, @name="first">
 => nil 
2.3.0 :013 > summary2 = SummaryRow.new
 => #<SummaryRow:0x00000001c4e9a0> 
2.3.0 :014 > summary3 = SummaryRow.new
 => #<SummaryRow:0x00000001c97a88> 
2.3.0 :015 > summary2.user_id = 2; summary1.name = 'second'
 => "second" 
2.3.0 :016 > summary3.user_id = 3; summary3.name = 'third'
 => "third" 
2.3.0 :017 > summary2.user_id = 2; summary2.name = 'second'
 => "second" 
2.3.0 :018 > summary1.user_id = 1; summary1.name = 'first'
 => "first" 
2.3.0 :019 > rows = [ summary1, summary2, summary3 ]
 => [#<SummaryRow:0x00000001b90068 @user_id=1, @name="first">, #<SummaryRow:0x00000001c4e9a0 @user_id=2, @name="second">, #<SummaryRow:0x00000001c97a88 @user_id=3, @name="third">] 
2.3.0 :020 > rows2 = Array.new
 => [] 
2.3.0 :021 > rows2 << rows.inject(:+)
 => [#<SummaryRow:0x00000001c24290 @user_id=1, @name="first">] 
2.3.0 :022 > puts rows2
#<SummaryRow:0x00000001c24290>
 => nil 
2.3.0 :023 >