Map an array modifying only elements matching a certain condition

Question

In Ruby, what is the most expressive way to map an array in such a way that certain elements are modified and the others left untouched?

This is a straight-forw

Answer 1

I've found that the best way to accomplish this is by using tap

arr = [1,2,3,4,5,6]
[].tap do |a|
  arr.each { |x| a << x if x%2==0 }
end