From: Eric Mahurin <eric_mahurin@...>
Date: 2005-07-16T11:58:54+09:00
Subject: Re: Cascading <=> comparisons



--- Garance A Drosehn <drosihn@gmail.com> wrote:

> Let's say I have a hash with some values in it, and I want to
> print out that hash in some sort order.  I can:
> 
> korder = vals.keys.sort { |ka, kb|
>     vals[kb] <=> vals[ka]
> }
> korder.each { |key| printf " %3d - %s\n", vals[key], key }
> 
> That's pretty easy, but what if I want to cascade comparisons
> in that sort, such that if the data-values are equal, then I
> want
> the sort order to be based on some other comparison?  It
> seems to me that I have to:
> 
> korder = vals.keys.sort { |ka, kb|
>     sres = vals[kb] <=> vals[ka]
>     sres = ka <=> kb    if sres == 0
>     sres
> }
> korder.each { |key| printf " %3d - %s\n", vals[key], key }
> 
> In perl, I can just casade the '<=>' comparisons, because it
> will treat the zero value as "false".  Thus, I could get away
> with a one-liner somewhat similar to:
> 
> vals[kb] <=> vals[ka] or a <=> kb
> 
> but that doesn't work in ruby.  Is there some other way I
> could
> collapse multiple <=> comparisons into a single statement?
> I do not mind the multi-statement form (now that I've
> convinced
> myself that I can't cascade them the way I could in perl),
> but I'm
> just wondering if there's a better way to do it.


(vals[kb] <=> vals[ka]).nonzero? or a <=> kb



		
____________________________________________________
Start your day with Yahoo! - make it your home page 
http://www.yahoo.com/r/hs