Doesn't zip basically do that already?

ruby-1.9.2-p180 :001 > l = [1,2,3]; r = [6,5,4]
 => [6, 5, 4]
ruby-1.9.2-p180 :002 > arr = []; l.zip(r) { |first, second| arr << 3 *
first + second }; arr
 => [9, 11, 13]

(Are you just trying to save the last step?)

~ jf
--
John Feminella
Principal Consultant, BitsBuilder
LI: http://www.linkedin.com/in/johnxf
SO: http://stackoverflow.com/users/75170/