From: John Joyce <dangerwillrobinsondanger@...>
Date: 2007-10-18T01:21:37+09:00
Subject: Re: sort_by


On Oct 17, 2007, at 10:55 AM, mortee wrote:

> Paulo Carvalho wrote:
>> Hello
>>
>> I have a list of rows which I want to order by a column.
>> I make it with
>> @values_ordered = @values.sort_by(&:id_column)
>>
>> What if I want to inverse the order (like order by x desc in SQL)
>>
>> How could I do that using sort_by? is that possible?
>
> what about
>
> @values_ordered = @values.sort_by { |e| -e.id_column }
>
> mortee
>
>
Is it Rails?  If so, ActiveRecord has a way to do this with a  
database table's values by using a hash option, order => DESC
If you're using a database, you should consider ActiveRecord itself.
There is also Ruby DBI, which allows pretty much plain SQL action.
Either one will make life much easier working with a database.
There is also OG (another ORM)

The question I have is, Is your list of rows a multi-dimensional Array?
If so, and I am assuming it is, you can use the Array indices like  
columns for sort_by
Use irb (and ri to check some docs) to compare :
Array.sort
Array.sort { |a, b| block }

sort can also take a block and might be what you want.
a = [ "d", "a", "e", "c", "b" ]
a.sort                          #=> ["a", "b", "c", "d", "e"]
a.sort {|x,y| y <=> x }   #=> ["e", "d", "c", "b", "a"]