How do I sort a Ruby array of strings by length?

Question

How do I sort this:

arr = ["aaa","aa","aaaa","a","aaaaa"]; 

Into this?

arr = ["a","aa","aaa","aaaa","aaaaa"]; 

Answer 1

arr = arr.sort_by {|x| x.length} 

Or in 1.8.7+:

arr = arr.sort_by(&:length)