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Hash/2-d array help!

Just Maz

12/14/2006 6:23:00 PM

Would anyone happen to know how would I go about creating a hash where I
have more then one value equating to another?
i.e. England => Liverpool, England => London, France =>Rennes,
England=>Plymouth, France=>Paris.

I've tried all sorts of ways to do this but I always seem to overwrite
the old value of hash[england]=liverpool when I try and add London to
england too.
Is this even possible using a conventional hash? Or would I somehow have
to use a hash of arrays or something?
Also...Just how would I recall the values once I have them?
In my experiments I may well have stumbled across the answer but can't
retrieve them.

Sorry for this question being rather vague but I don't even know the
name of what I'm trying to do or anything about how to do it..I'd
appreciate any help here, at the very least even just a pointer in the
right direction.

--
Posted via http://www.ruby-....
7 Answers

Christopher Schneider

12/14/2006 6:41:00 PM

0

If you're doing it incrementally, instead of all at once like
demonstrated, the same end product can be done like:

hash = Hash.new

# LOOP
hash[key] ||= Array.new
hash[key] << value
# END LOOP

Just put the appropriate looping mechanism around those 2 lines, and
define key and value (ie England=key, and Liverpool=value).

-Chris

On Dec 14, 2006, at 11:28 AM, Jason Roelofs wrote:

> hash = {
> England => [Liverpool, London, Plymouth],
> France => [Rennes, Paris]
> }
>
> Jason
>
> On 12/14/06, Just Maz <josquius@hotmail.com> wrote:
>>
>> Would anyone happen to know how would I go about creating a hash
>> where I
>> have more then one value equating to another?
>> i.e. England => Liverpool, England => London, France =>Rennes,
>> England=>Plymouth, France=>Paris.
>>
>> I've tried all sorts of ways to do this but I always seem to
>> overwrite
>> the old value of hash[england]=liverpool when I try and add London to
>> england too.
>> Is this even possible using a conventional hash? Or would I
>> somehow have
>> to use a hash of arrays or something?
>> Also...Just how would I recall the values once I have them?
>> In my experiments I may well have stumbled across the answer but
>> can't
>> retrieve them.
>>
>> Sorry for this question being rather vague but I don't even know the
>> name of what I'm trying to do or anything about how to do it..I'd
>> appreciate any help here, at the very least even just a pointer in
>> the
>> right direction.
>>
>> --
>> Posted via http://www.ruby-....
>>
>>

Just Maz

12/14/2006 6:45:00 PM

0

Jason Roelofs wrote:
> hash = {
> England => [Liverpool, London, Plymouth],
> France => [Rennes, Paris]
> }
>
> Jason

Ah....now that's a lot simpler then I thought.
How would I then retrieve these values?

puts hash gives error as does puts hash[England] or puts
hash{England}...Are they counted in anyway like hash{england[1]}?

--
Posted via http://www.ruby-....

Paul Lutus

12/14/2006 6:51:00 PM

0

Just Maz wrote:

> Jason Roelofs wrote:
>> hash = {
>> England => [Liverpool, London, Plymouth],
>> France => [Rennes, Paris]
>> }
>>
>> Jason
>
> Ah....now that's a lot simpler then I thought.
> How would I then retrieve these values?
>
> puts hash gives error as does puts hash[England] or puts
> hash{England}...Are they counted in anyway like hash{england[1]}?

If you create a hash as the prior poster described:

>> hash = {
>> England => [Liverpool, London, Plymouth],
>> France => [Rennes, Paris]
>> }

Then you retrieve an ordinary array (not a hash) by using one of the keys:

array = hash["England"]

Now "array" contains [Liverpool, London, Plymouth], and you retrieve one of
them using an index number -- array[0] retrieves "Liverpool".

--
Paul Lutus
http://www.ara...

Just Maz

12/14/2006 10:39:00 PM

0

Ah! Thanks. Got it totally working now!

One other minor thing- would it be possible for the the strings inside
'France' => ['Rennes', 'Paris']
to be variables instead?

i.e. instead of France= those two I earlier have a 'enter country name'
and 'enter city 1', 'enter city 2',etc...


Off the top of my head I think there may be some sort of symbol you'd
put before nation to show it is a actual stored string but I can't
remember what it was...

--
Posted via http://www.ruby-....

Paul Lutus

12/14/2006 10:59:00 PM

0

Just Maz wrote:

> Ah! Thanks. Got it totally working now!
>
> One other minor thing- would it be possible for the the strings inside
> 'France' => ['Rennes', 'Paris']
> to be variables instead?

Yes, certainly. You can easily create an array containing variables instead
of literal strings.

> Off the top of my head I think there may be some sort of symbol you'd
> put before nation to show it is a actual stored string but I can't
> remember what it was...

Not in Ruby. Ruby doesn't have characters in variable names that give away
their type.

--
Paul Lutus
http://www.ara...

Li Chen

12/14/2006 11:04:00 PM

0

Just Maz wrote:
> Ah! Thanks. Got it totally working now!
>
> One other minor thing- would it be possible for the the strings inside
> 'France' => ['Rennes', 'Paris']
> to be variables instead?
>
> i.e. instead of France= those two I earlier have a 'enter country name'
> and 'enter city 1', 'enter city 2',etc...
>
>
> Off the top of my head I think there may be some sort of symbol you'd
> put before nation to show it is a actual stored string but I can't
> remember what it was...


Hi,

Is the following what you try to do?


Li

##script
#:england and :france (or :England and :France) are symbols in ruby

liverpool='Liverpool'
london='London'
plymouth='Pymouth'
rennes='Rennes'
paris='Paris'


hash = {
:england => [liverpool, london, plymouth],
:france => [rennes, paris]
}

puts hash.fetch(:england)[0]
puts hash.fetch(:england)[2]

#output
>ruby forum3.rb
Liverpool
Pymouth
>Exit code: 0

--
Posted via http://www.ruby-....

Just Maz

12/14/2006 11:11:00 PM

0

Oh right thanks, got it working.
It turns out I'd just forgot to change the puts statement to puts
nation...*jumps from metaphorical window*

I think its about time I took a break from staring at a computer screen
for one day.

--
Posted via http://www.ruby-....