From: Robert Klemme <shortcutter@...>
Date: 2007-07-17T06:21:56+09:00
Subject: Re: clean nice way (hash)

On 16.07.2007 20:15, James Edward Gray II wrote:
> On Jul 16, 2007, at 12:10 PM, Robert Klemme wrote:
> 
>> On 16.07.2007 17:03, James Edward Gray II wrote:
>>> On Jul 16, 2007, at 9:36 AM, Robert Klemme wrote:
>>>> 2007/7/16, Chris Carter <cdcarter@gmail.com>:
>>>>> On 7/16/07, James Edward Gray II <james@grayproductions.net> wrote:
>>>>> > On Jul 16, 2007, at 5:58 AM, hemant wrote:
>>>>> >
>>>>> > > a.inject({}) {|mem,(key,value)| mem[key] = {'name' => value}; 
>>>>> mem }
>>>>> >
>>>>> > I would write that as:
>>>>> >
>>>>> >    a.inject(Hash.new) { |h, (k, v)| h.merge(k => v) }
>>>>> >
>>>>> > James Edward Gray II
>>>>> >
>>>>> >
>>>>>
>>>>> But that doesn't yield what he wanted... You could do
>>>>> a.inject(Hash.new){|h,(k,v)| h.merge(k => { 'name' => value})}
>>>>
>>>> Still it's inefficient because of all the small Hashes that are thrown
>>>> away immediately. The solution provided by hemant is better although
>>>> not as elegant.
>>> If that bothers you, change merge() to merge!().
>>
>> ... which doesn't help because it does not avoid all those one pair 
>> hashes. :-)
> 
> I did eliminate some Hashes, those created for each iteration inject(), 
> so I feel it's wrong to say it didn't help.  You are right about the 
> parameter Hashes though.

Those were the ones I referred to originally.  And yes, "did not help" 
was only partly true. ;-)

> I do feel nitpicking something like this is squarely in the domain of 
> premature optimization though.  It's GC's job to lose sleep over the 
> objects I create, not mine.  I don't need to get involved until it looks 
> like GC is getting behind.  Those are my feelings on the matter.

I think I understand your point and as a geneal statement I even do 
agree.  However, another general statement that I'd add to the mix is 
"do not make superfluous work if you can avoid it easily".  For me this 
is such a case: we just get a slightly more elegant solution by using 
#merge because we do not need to mention the Hash to make #inject happy, 
but we force the machine to do a lot of extra work (how much remains to 
be measured).  It's not exactly a comparable case but if I have a tree 
where data is stored with a particular order I would not do a full 
traversal when searching for a specific element (O(n)); instead I'd use 
an algorith that's aware of the tree structure and the ordering (O(log(n))).

Kind regards

	robert