hash of hashes

[Paul Argentoff]

Hi all.

How can I create $Subject for future population?
--
Yours truly, WBR, Paul Argentoff.
Jabber: [email]paul@jabber.rtelekom.ru[/email]
RIPE: PA1291-RIPE

[Paul Argentoff]

On Friday 03 October 2003 14:04, Paul Argentoff wrote:

> How can I create $Subject for future population?

Let's put it this way: I need to create a nested hash which will be populated
later by referencing the keys in the subhashes. How can I do this?
--
Yours truly, WBR, Paul Argentoff.
Jabber: [email]paul@jabber.rtelekom.ru[/email]
RIPE: PA1291-RIPE

[Emmanuel Touzery]

Paul Argentoff wrote:

>On Friday 03 October 2003 14:04, Paul Argentoff wrote:
>
>
>

>>How can I create $Subject for future population?
>>
>>

>
>Let's put it this way: I need to create a nested hash which will be populated
>later by referencing the keys in the subhashes. How can I do this?
>
>

not sure i understand your question. does this help you?

irb(main):001:0> a = {}
{}
irb(main):002:0> a["blue"] = {}
{}
irb(main):003:0> a["blue"]["red"] = 3
3
irb(main):004:0> a["blue"]
{"red"=>3}
irb(main):005:0> a["blue"]["red"]
3
irb(main):006:0>

[Paul Argentoff]

On Friday 03 October 2003 14:48, Emmanuel Touzery wrote:

> irb(main):001:0> a = {}
> {}
> irb(main):002:0> a["blue"] = {}
> {}
> irb(main):003:0> a["blue"]["red"] = 3
> 3
> irb(main):004:0> a["blue"]
> {"red"=>3}
> irb(main):005:0> a["blue"]["red"]
> 3
> irb(main):006:0>

I need something like this:

a = {{}} # this doesn't work, but i've just written it here to emph. the
# subject
...
# somewhere in the iteration
a[foo][bar] = baz
...
--
Yours truly, WBR, Paul Argentoff.
Jabber: [email]paul@jabber.rtelekom.ru[/email]
RIPE: PA1291-RIPE

[Emmanuel Touzery]

Paul Argentoff wrote:

>On Friday 03 October 2003 14:48, Emmanuel Touzery wrote:
>
>
>

>>irb(main):001:0> a = {}
>>{}
>>irb(main):002:0> a["blue"] = {}
>>{}
>>irb(main):003:0> a["blue"]["red"] = 3
>>3
>>irb(main):004:0> a["blue"]
>>{"red"=>3}
>>irb(main):005:0> a["blue"]["red"]
>>3
>>irb(main):006:0>
>>
>>

>
>I need something like this:
>
>a = {{}} # this doesn't work, but i've just written it here to emph. the
> # subject
>...
># somewhere in the iteration
>a[foo][bar] = baz
>...
>
>

i think you need ruby 1.8's block form for creating hashes. i asked that
question recently, and here is the snippet from Guy Decoux:

svg% ruby -e 'has = Hash.new {|h,k| h[k]={}}; has["blue"]["red"] = 1; p has'
{"blue"=>{"red"=>1}}
svg%

[Paul Argentoff]

On Friday 03 October 2003 14:48, Emmanuel Touzery wrote:

> not sure i understand your question. does this help you?
>
> irb(main):001:0> a = {}
> {}
> irb(main):002:0> a["blue"] = {}
> {}
> irb(main):003:0> a["blue"]["red"] = 3
> 3
> irb(main):004:0> a["blue"]
> {"red"=>3}
> irb(main):005:0> a["blue"]["red"]
> 3
> irb(main):006:0>

Here is my example:

irb(main):008:0> a = Hash.new(Hash.new(Array.new(2,0)))
=> {}
irb(main):009:0> a['foo']['bar'][1] = 2
=> 2
irb(main):010:0> a['foo']['bar']
=> [0, 2]
irb(main):011:0> a.keys
=> []
irb(main):012:0>

After this I can't iterate over a's keys -- what I've written the whole mess
for
--
Yours truly, WBR, Paul Argentoff.
Jabber: [email]paul@jabber.rtelekom.ru[/email]
RIPE: PA1291-RIPE

[Austin Ziegler]

On Fri, 3 Oct 2003 20:17:50 +0900, Paul Argentoff wrote:

> On Friday 03 October 2003 14:48, Emmanuel Touzery wrote:

>> not sure i understand your question. does this help you?

> Here is my example:
> irb(main):008:0> a = Hash.new(Hash.new(Array.new(2,0)))

This won't work because you're not doing what you're expecting. What
you're saying is that a nil key will return a particular Hash where
nil keys return a particular array.

This would be like saying:

arry = Array.new(2, 0)
hash = Hash.new(arry)
a = Hash.new(hash)

a['foo'] # => hash
a['foo']['bar'] # => arry

What you want is:

a = Hash.new do |h, k|
h[k] = Hash.new do |h1, k1|
h1[k1] = Array.new(2, 0)
end
end

This only works with 1.8 or bettter. Ruby does not auto-vivify
hashes or arrays like Perl. Note further that if you do something
like:

a = Hash.new { |h, k| h[k] = :val; nil }

You will get a perhaps surprising -- but entirely correct -- result:

a['foo'] # => nil
a['foo'] # => :val

When you attempt to access a nonexistant hash key, the default value
is returned. In this case, it's nil. However, in the block you have
also set a side effect of setting the hash key provided to :val, so
the next time you access 'foo', it's no longer nonexistant.

-austin
--
austin ziegler * [email]austin@halostatue.ca[/email] * Toronto, ON, Canada
software designer * pragmatic programmer * 2003.10.03
* 09.15.49

[Joel VanderWerf]

Paul Argentoff wrote:
...

> I need something like this:
>
> a = {{}} # this doesn't work, but i've just written it here to emph. the
> # subject
> ...
> # somewhere in the iteration
> a[foo][bar] = baz
> ...

hash_maker = proc do |h, k|
h[k] = Hash.new(&hash_maker)
end

h = Hash.new(&hash_maker)

h[1][2][3][4][5] = 6

p h # {1=>{2=>{3=>{4=>{5=>6}}}}}

[Paul Argentoff]

On Friday 03 October 2003 18:37, Joel VanderWerf wrote:

> hash_maker = proc do |h, k|
> * *h[k] = Hash.new(&hash_maker)
> end

)) Exmaple is worthy of a Haskell tutorial ))

The problem is, afaik, that I tried to do THAT with Ruby 1.6 :-/
--
Yours truly, WBR, Paul Argentoff.
Jabber: [email]paul@jabber.rtelekom.ru[/email]
RIPE: PA1291-RIPE

[Joel VanderWerf]

Paul Argentoff wrote:

> On Friday 03 October 2003 18:37, Joel VanderWerf wrote:
>
>

>>hash_maker = proc do |h, k|
>> h[k] = Hash.new(&hash_maker)
>>end

>
>
> )) Exmaple is worthy of a Haskell tutorial ))
>
> The problem is, afaik, that I tried to do THAT with Ruby 1.6 :-/

It might work with the shim module, from RAA.

[Austin Ziegler]

On Sat, 4 Oct 2003 10:52:51 +0900, Dave Brown wrote:

> In article <200310031434.31907.argentoff@rtelekom.ru>,
> Paul Argentoff <argentoff@rtelekom.ru> wrote:
> : On Friday 03 October 2003 14:04, Paul Argentoff wrote:
> : > How can I create $Subject for future population?
> : Let's put it this way: I need to create a nested hash which will be
> : populatedlater by referencing the keys in the subhashes. How can I do
> : this?

> You mean, er,

> irb(main):001:0> a=Hash.new({})
> => {}
> irb(main):002:0> a['foo']
> => {}

I don't think that's what you want:

irb(main):001:0> a = Hash.new({})
=> {}
irb(main):002:0> a['foo'].id
=> 21054224
irb(main):003:0> a['bar'].id
=> 21054224

-austin
--
austin ziegler * [email]austin@halostatue.ca[/email] * Toronto, ON, Canada
software designer * pragmatic programmer * 2003.10.03
* 22.22.45

[Joel VanderWerf]

Dave Brown wrote:

> In article <200310031434.31907.argentoff@rtelekom.ru>,
> Paul Argentoff <argentoff@rtelekom.ru> wrote:
> : On Friday 03 October 2003 14:04, Paul Argentoff wrote:
> :
> : > How can I create $Subject for future population?
> :
> : Let's put it this way: I need to create a nested hash which will be populated
> : later by referencing the keys in the subhashes. How can I do this?
>
> You mean, er,
>
> irb(main):001:0> a=Hash.new({})
> => {}
> irb(main):002:0> a['foo']
> => {}
>
> ?
>
> --Dave

That's like, a real bad trip, dude:

irb(main):002:0> a=Hash.new({})
=> {}
irb(main):003:0> a[1]
=> {}
irb(main):004:0> a[1]["x"] = "y"
=> "y"
irb(main):005:0> a
=> {}
irb(main):006:0> a[1]
=> {"x"=>"y"}
irb(main):007:0> a[1] = 2
=> 2
irb(main):008:0> a[2]
=> {"x"=>"y"}
irb(main):009:0> a[1]
=> 2

It would help to do

a = Hash.new {{}}

since you get a new hash each time...

[Martin DeMello]

Joel VanderWerf <vjoel@path.berkeley.edu> wrote:

>
> hash_maker = proc do |h, k|
> h[k] = Hash.new(&hash_maker)
> end
>
> h = Hash.new(&hash_maker)
>
> h[1][2][3][4][5] = 6
>
> p h # {1=>{2=>{3=>{4=>{5=>6}}}}}

My head hurts That needs to go on the Ruby Idioms page.

martin

[Simon Strandgaard]

On Sat, 04 Oct 2003 06:25:35 +0000, Martin DeMello wrote:

> Joel VanderWerf <vjoel@path.berkeley.edu> wrote:

>>
>> hash_maker = proc do |h, k|
>> h[k] = Hash.new(&hash_maker)
>> end
>>
>> h = Hash.new(&hash_maker)
>>
>> h[1][2][3][4][5] = 6
>>
>> p h # {1=>{2=>{3=>{4=>{5=>6}}}}}

>
> My head hurts That needs to go on the Ruby Idioms page.

Wew nice trick indeed :-)

I have added it to the StandardClassExtension page:
[url]http://www.rubygarden.org/ruby?StandardClassExtensions/Hash[/url]

--
Simon Strandgaard

[Robert Klemme]

"Paul Argentoff" <argentoff@rtelekom.ru> schrieb im Newsbeitrag
news:200310031517.45708.argentoff@rtelekom.ru...

> On Friday 03 October 2003 14:48, Emmanuel Touzery wrote:
>

> > not sure i understand your question. does this help you?
> >
> > irb(main):001:0> a = {}
> > {}
> > irb(main):002:0> a["blue"] = {}
> > {}
> > irb(main):003:0> a["blue"]["red"] = 3
> > 3
> > irb(main):004:0> a["blue"]
> > {"red"=>3}
> > irb(main):005:0> a["blue"]["red"]
> > 3
> > irb(main):006:0>

>
> Here is my example:
>
> irb(main):008:0> a = Hash.new(Hash.new(Array.new(2,0)))
> => {}
> irb(main):009:0> a['foo']['bar'][1] = 2
> => 2
> irb(main):010:0> a['foo']['bar']
> => [0, 2]
> irb(main):011:0> a.keys
> => []
> irb(main):012:0>
>
> After this I can't iterate over a's keys -- what I've written the whole

mess

> for

That's because the form Hash.new( obj ) just replaces the nil return value
for keys that are not found. In your example you have a hash that returns a
hash for unknown keys that in turn returns an array for unknown keys. You
definitely need the block form. Or you have to wrap or sub class the hash
if you want to use pre 1.8 ruby versions.

Regards

robert

[Robert Klemme]

"Joel VanderWerf" <vjoel@PATH.Berkeley.EDU> schrieb im Newsbeitrag
news:3F7E3AF2.2050701@path.berkeley.edu...

> Dave Brown wrote:

> > In article <200310031434.31907.argentoff@rtelekom.ru>,
> > Paul Argentoff <argentoff@rtelekom.ru> wrote:
> > : On Friday 03 October 2003 14:04, Paul Argentoff wrote:
> > :
> > : > How can I create $Subject for future population?
> > :
> > : Let's put it this way: I need to create a nested hash which will be

populated

> > : later by referencing the keys in the subhashes. How can I do this?
> >
> > You mean, er,
> >
> > irb(main):001:0> a=Hash.new({})
> > => {}
> > irb(main):002:0> a['foo']
> > => {}
> >
> > ?
> >
> > --Dave

>
> That's like, a real bad trip, dude:
>
> irb(main):002:0> a=Hash.new({})
> => {}
> irb(main):003:0> a[1]
> => {}
> irb(main):004:0> a[1]["x"] = "y"
> => "y"
> irb(main):005:0> a
> => {}
> irb(main):006:0> a[1]
> => {"x"=>"y"}
> irb(main):007:0> a[1] = 2
> => 2
> irb(main):008:0> a[2]
> => {"x"=>"y"}
> irb(main):009:0> a[1]
> => 2
>
> It would help to do
>
> a = Hash.new {{}}
>
> since you get a new hash each time...

Not really:

irb(main):001:0> h=Hash.new{{}}
=> {}
irb(main):002:0> h[1][2]="foo"
=> "foo"
irb(main):003:0> h
=> {}
irb(main):004:0>

You need a = Hash.new {|h,k| h[k]={}} as pointed out already.

robert

>
>

[Joel VanderWerf]

Robert Klemme wrote:

> "Joel VanderWerf" <vjoel@PATH.Berkeley.EDU> schrieb im Newsbeitrag

...

>>It would help to do
>>
>>a = Hash.new {{}}
>>
>>since you get a new hash each time...

>
>
> Not really:

Oops. Of course you're right, since the value returned by the block is
never assigned to any part of the hash. You always have to do that yourself.

[Robert Klemme]

"Joel VanderWerf" <vjoel@PATH.Berkeley.EDU> schrieb im Newsbeitrag
news:3F7F0FF8.1030708@path.berkeley.edu...

> Robert Klemme wrote:

> > "Joel VanderWerf" <vjoel@PATH.Berkeley.EDU> schrieb im Newsbeitrag

> ..

> >>It would help to do
> >>
> >>a = Hash.new {{}}
> >>
> >>since you get a new hash each time...

> >
> >
> > Not really:

>
> Oops. Of course you're right, since the value returned by the block is
> never assigned to any part of the hash. You always have to do that

yourself.

.... and it's always the same. Something not wanted in this case.

robert

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Umm... this sounds suspiciously like a homework assignment.