Many solutions, different efficiencies

I compared 3 ways of creating even-squares of numbers in Ruby, and the fastests seems to be 'map {} .compact!'. Here are the methods, each performed 1,000,000 times:

1: (1..10).inject( Array.new )
          { |a, i| a << i * i if i % 2 == 0; a }
2: (1..10).select { |i| i % 2 == 0 }.collect { |i| i * i }
3: (1..10).map { |i| i * i if i % 2 == 0 }.compact!

and here are the results:

         user     system      total        real
1:  31.734000   0.015000  31.749000 ( 31.956000)
2:  22.313000   0.000000  22.313000 ( 22.416000)
3:  19.890000   0.000000  19.890000 ( 19.976000)

The first one is probably the most memory efficient, while the last is probably the least memory efficient. Fast, Cheap, Good - pick *two* ;)