From: Wayne Brissette <waynefb@...>
Date: 2011-11-05T02:49:34+09:00
Subject: What happens in dual sorts with nil values?

I've put together an array that has a map. I did this so I could do some multi-level sorting of data. For example, if I had a map with: 

Struct.new(:first, :last, :age)

And let's say I only had some of the ages, so some values were nil. 

Doing a multi-level sort using

person.sort_by! { |a| [a.last, a.first, a.age]}

gives me a list sorted correctly by last name, then first, and age?? (maybe, I need to test more)

If I put the sort_by with a.age first, then I get an error. 

`block in <top (required)>': undefined local variable or method `ball_map' for main:Object (NameError)

I'm assuming this is because I'm trying to sort integers and have one with a nil value. So my question really is two-fold. Can I sort based on age if some values are nil? (doesn't look like it), and second, am I fooling myself into thinking that I'm sorting on a.age when it's not the first sort value? 

Wayne