Grab only the latest comment

Hi all

In a typical User - Post - Comment model in Rails, every user can
create a Post and also can create Comment, question is how to grab
every user latest comment on specific post.

Example:

Post A have 3 user making comment
User 1 have 5 comment
User 2 have 6 comment
User 3 have 2 comment

So the view I want is just the latest comment for every user:

Post A have 3 user making
User 1 latest comment
User 2 latest comment
user 3 latest comment

How to do it ?

thanks

http://api.rubyonrails.org/classes/ActiveRecord/Base.html