title: Removing fields with Ruby
body: <p>Usually to remove some fields from collections in MongoDB, <code>$unset</code> is used.  What can I do in Ruby to accomplish that? I have tried to read <a href="http://api.mongodb.org/ruby/current/Mongo/Collection.html#remove-instance_method" rel="nofollow">this</a>, but I couldn't understand how to use it. I am new to Ruby and still learning to work with it.</p>