What class this "map function" should be method of?

I'm not sure this is the most elegant way...

a = [1,2,3]
b = [4,5,6]
c = []         # the result

a.each_with_index{|e,i| c << [e,b[i]] }

'Enumerable#collect' is the closest method to Python's function 'map'. There
is synonim 'Enumerable#map' ;)

c = b.collect{|e| -e}