From: Martin DeMello <martindemello@...>
Date: 2004-08-17T18:00:58+09:00
Subject: Re: Q: Shifting a hash anf and array

Robert Klemme <bob.news@gmx.net> wrote:
 >
> > Hash[*(hash.keys.rot1.zip(hash.values.rot1).flatten)]
> 
> Hm, IMHO there is one "rot1" too much: you're rotating keys *and* values
> while you should only rotate one of them.  Otherwise I figure the result
> will be the same as the original hash... :-)

Doh :)

> The other drawback of your solution is that it relys on #keys and #values
> returning elements in matching order, i.e., if you zip both you get the same
> hash.  Although that might work it makes me feel a bit wary because AFAIK
> it's not a guaranteed property of Hash (and I wouldn't want to rely on it).
> This might even change over time if the Hash implementation was changed for
> any reasons.

I know, but that was the only way I could think of to avoid the
one-lookup-per-key.

> How about these one liners, that avoids the problem:
> 
> h = {0=>"a", 1=>"b", 2=>"c"}
> # put rotated in h2
> (h2={}).send(:[]=, *h.sort.inject {|(k1,v1),(k2,v2)| h2[k1]=v2; [k2, v1]})
> # rotate inplace
> h.send(:[]=, *h.sort.inject {|(k1,v1),(k2,v2)| h[k1]=v2; [k2, v1]})

Neat - I didn't know there was a Hash#sort

martin