Forum: Ruby Access Hash in the same order that was created

I need to access to a Hash in the same order that It was created:

mh=Hash.new()
mh["one"]="1"
mh["two"]="2"
mh["three"]="3"
mh["four"]="4"

mh.each {|val|
  puts val[0]
}

In this example I get:
three
two
one
four

and I would like to get:
one
two
three
four


is that possible?

Thanks

Mario Ruiz wrote:
> I need to access to a Hash in the same order that It was created:
> is that possible?
> 
> Thanks

No.

On May 15, 2008, at 10:22 AM, Mario Ruiz wrote:

> }
> three
> four
>
>
> is that possible?
>
> Thanks




gem install orderedhash

mh = OrderedHash.new
...
...


etc.

a @ http://codeforpeople.com/

On May 15, 2008, at 10:22 AM, Mario Ruiz wrote:

> is that possible?

forgot to mention - 1.9 does this by default now.

a @ http://codeforpeople.com/

ara.t.howard wrote:
> is that possible?

Hash preserves insertion order in Ruby 1.9

irb(main):026:0> RUBY_VERSION
=> "1.9.0"
irb(main):027:0> mh.each{|val| puts val[0]}
one
two
three
four

regards,
Tor Erik

On Fri, May 16, 2008 at 01:22:56AM +0900, Mario Ruiz wrote:
> I need to access to a Hash in the same order that It was created:
[...]
> is that possible?

First off, this is not a hash. Hashes are inherently unordered. Hashes
provide amortized O(1) insertion and retrieval of elements by key, and
that's it. If you need an ordered set of pairs, use an array of arrays.
Yes, this is a pet peeve of mine.

There was an OrderedHash that someone wrote, but needing it is an
indication of a design problem. It has also been obsoleted by the
Dictionary in Ruby Facets.

One could argue that, like Java, there should be a standard Dictionary
interface that Hash implements, and that there should be another
implementation that preserves order without guaranteeing anything about
performance. That's not how things stand right now.

> Thanks
--Greg

> mh["two"]="2"
> one
> four
>
> and I would like to get:
> one
> two
> three
> four
>
>
> is that possible?

No way with standard Hash, and it shouldn't be really. You can use an 
array instead of a hash, and Array#assoc to retrieve entries based on 
keys.

Gennady.

* Mario Ruiz <mario@betware.com> (18:22) schrieb:

> }
> three
> four
>
>
> is that possible?

The Hash doesn't remember the order in which you put the values in.

If the order is important not easily reconstructable, you have to
store the keys in an Array.

mfg,                      simon .... l

Thanks to everybody