Rails spinoffs - Jul 2007 - Object Property Sorting - Hash?

I''m trying to sort an object by its property names.  As I understand
it,
iterating over an object using for...in or using Hash.each() (or
Hash.sortBy()) does not guarantee the order of the properties.

Is there an easy and low-overhead way to guarantee order?  Or would I
need to have some type of collection object that uses arrays instead of
the property-value configuration that Hash uses?

Here is an example object similar to the one I want to sort:

var foodsByLetter = {
  ''B'': [''broccoli'',
''bread''],
  ''C'': [''carrots'',
''celery''],
  ''A'': [''alfalfa sprouts'',
''apple'']
};

Then I want to sort by the object''s keys so I can create a nested list:
<ul>
  <li>A<ul><li>alfalfa
sprouts</li><li>apple</li></ul></li>
 
<li>B<ul><li>broccoli</li><li>bread</li></ul></li>
 
<li>C<ul><li>carrots</li><li>celery</li></ul></li>
</ul>

So for example, I could do $H(foodsByLetter).keys().sort(); to sort the
keys alphabetically but then I wouldn''t know which letter related to
which food list.

Any help is appreciated.

-- Ken Snyder


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On Jul 3, 4:44 am, Ken Snyder
<kendsny...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> I''m trying to sort an object by its property names.  As I
understand it,
> iterating over an object using for...in or using Hash.each() (or
> Hash.sortBy()) does not guarantee the order of the properties.
>
> Is there an easy and low-overhead way to guarantee order?
No.  The ECMAScript Language Specification says:

8.6 The Object Type
"An Object is an unordered collection of properties. Each property
consists of a name, a value and a set of attributes."

12.6.4 For-in statement
"The mechanics of enumerating the properties (step 5 in the first
algorithm, step 6 in the second) is implementation dependent. The
order of enumeration is defined by the object."

In other words, you can''t depend on the properties of an object being
returned in any particular order for different browsers.  You might
like to get the names (say using for..in) and push them in an array,
use Array.prototype.sort() to sort them, then use that order to get
the property values.

If order is important, perhaps the values should be stored in an
array.

--
Rob


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RobG wrote:
> In other words, you can''t depend on the properties of an object
being
> returned in any particular order for different browsers.  You might
> like to get the names (say using for..in) and push them in an array,
> use Array.prototype.sort() to sort them, then use that order to get
> the property values.
>
> ...
Very helpful.  I think that is what I was missing.

Thanks,

Ken


var foodsByLetter = {
  ''B'': [''broccoli'',
''bread''],
  ''C'': [''carrots'',
''celery''],
  ''A'': [''alfalfa sprouts'',
''apple'']
};

Instead of:
for( var letter in foodsByLetter ) {
  // out of order
  foodsByLetter[letter];
}

I can do:
Object.keys(foodsByLetter).sort().each(function(letter) {
  foodsByLetter[letter];
});

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