From: Florian Gross <flgr@...>
Date: 2004-10-05T02:54:53+09:00
Subject: Re: How to sort a table in Ruby?

Gavin Kistner wrote:

>>>    a.sort { |x,y| x[3] <=> y[3] }    # sort on 4th element
>> That's even better:
>> a.sort_by {|row| row[3]}
> 
> The reason that #sort_by is better than #sort is described in the 
> documentation. In short (IIRC) it's because it caches the key values for 
> each row (performing the block only once for each row) and uses those to 
> sort, rather than invoking the block for every unique pair it has to 
> compare.
> 
> A downside, however, is the inability to specify something like a 
> reverse sort. (Although for that case you can just reverse the array 
> afterwards.)

It is possible when you want to sort by something that can be expressed 
as a number:

persons.sort_by { |person| -person.age }

Regards,
Florian Gross