Performance of Arrays and Hashes in Ruby

Question

I have a program that will store many instances of one class, let\'s say up to 10.000 or more. The class instances have several properties that I need from time to time, but

Answer 1

Ruby has a set class in its standard library, have you considering keeping an (additional) set of IDs only?

http://stdlib.rubyonrails.org/libdoc/set/rdoc/index.html

To quote the docs: "This is a hybrid of Array’s intuitive inter-operation facilities and Hash’s fast lookup".