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comp.lang.ruby

need: hierarchic data structure

Meinrad Recheis

2/21/2006 5:32:00 PM

hi,
i am searching for an implementation of a hierarchic datastructure that
behaves similar to a file system except that get of an inexistent path
returns nil and set of an unexistent path creates the required nodes
silently.

example:
d=HierarchicData.new

d[:foo, :bar] # => nil
d[:foo, :bar]=42
d[:foo, :bar] # => 42

d[:foo, :foo, 0, 1, :bar]=Object.new # creates a hash in an array in an
array in a hash in a hash

i want to check if this kind of data structure (or similar) has been
implemented already as library. if not i am going to do it.

thx for any comments!
-- henon
5 Answers

Logan Capaldo

2/21/2006 5:48:00 PM

0


On Feb 21, 2006, at 12:33 PM, henon wrote:

> hi,
> i am searching for an implementation of a hierarchic datastructure
> that
> behaves similar to a file system except that get of an inexistent path
> returns nil and set of an unexistent path creates the required nodes
> silently.
>
> example:
> d=HierarchicData.new
>
> d[:foo, :bar] # => nil
> d[:foo, :bar]=42
> d[:foo, :bar] # => 42
>
> d[:foo, :foo, 0, 1, :bar]=Object.new # creates a hash in an array
> in an
> array in a hash in a hash
>
> i want to check if this kind of data structure (or similar) has been
> implemented already as library. if not i am going to do it.
>
> thx for any comments!
> -- henon
>
>


Have you considered this?

class HierarchicData < Hash
def [](*args)
super(args)
end

def []=(*args)
keys = args[0..(args.length - 2)]
value = args.last
super(keys, value)
end
end


irb(main):012:0> d = HierarchicData.new
=> {}
irb(main):013:0> d[:foo, :bar]
=> nil
irb(main):014:0> d[:foo, :bar] = 42
=> 42
irb(main):015:0> d[:foo, :bar]
=> 42
irb(main):016:0> d[:foo, :foo, 0, 1, :bar] = Object.new
=> #<Object:0x315d24>

Robert Klemme

2/21/2006 6:02:00 PM

0


"henon" <meinrad.recheis@gmail.com> schrieb im Newsbeitrag
news:1140543137.277936.273070@o13g2000cwo.googlegroups.com...
> hi,
> i am searching for an implementation of a hierarchic datastructure that
> behaves similar to a file system except that get of an inexistent path
> returns nil and set of an unexistent path creates the required nodes
> silently.
>
> example:
> d=HierarchicData.new
>
> d[:foo, :bar] # => nil
> d[:foo, :bar]=42
> d[:foo, :bar] # => 42
>
> d[:foo, :foo, 0, 1, :bar]=Object.new # creates a hash in an array in an
> array in a hash in a hash
>
> i want to check if this kind of data structure (or similar) has been
> implemented already as library. if not i am going to do it.
>
> thx for any comments!

There is the usual idiom of nested hashes:

insert = lambda {|h,k| h[k] = Hash.new(&insert)}
tree = Hash.new(&insert)

Then you can do

>> tree[:foo][:bar]
=> {}
>> tree[:foo][:bar]=42
=> 42
>> tree
=> {:foo=>{:bar=>42}}

Of course you can wrap that in a single class:

class HT
def initialize
insert = lambda {|h,k| h[k] = Hash.new(&insert)}
@tree = Hash.new(&insert)
end

def [](*a)
a.inject(@tree) {|h,k| h[k]}
end

def []=(*a)
val = a.pop
key = a.pop
a.inject(@tree) {|h,k| h[k]}[key]=val
val
end
end

>> h[:foo, :bar]
=> {}
>> h
=> #<HT:0x101dc690 @tree={:foo=>{:bar=>{}}}>
>> h[:foo, :bar]=24
=> 24
>> h
=> #<HT:0x101dc690 @tree={:foo=>{:bar=>24}}>
>> h[:bar]=2345
=> 2345
>> h
=> #<HT:0x101dc690 @tree={:bar=>2345, :foo=>{:bar=>24}}>

HTH

robert

Meinrad Recheis

2/21/2006 6:14:00 PM

0

actually this yields a flat hash with array keys not a hierarchic one,
which is not what i want because it cannot be iterated in different
hierarchy levels

Meinrad Recheis

2/21/2006 8:21:00 PM

0

> There is the usual idiom of nested hashes:

sure there's no problem implementing it ... I guess it has been
implemented a thousand times by a thousand different people. i am
asking if anyone knows a library because it might feature iterators,
clever error handling code, etc. and it might be tested better than yet
annother quicky-hacky-implementation.

are there any libraries or prominent applications known?
thanks for response,
-- henon

Robert Klemme

2/22/2006 12:53:00 PM

0

henon <meinrad.recheis@gmail.com> wrote:
>> There is the usual idiom of nested hashes:
>
> sure there's no problem implementing it ... I guess it has been
> implemented a thousand times by a thousand different people. i am
> asking if anyone knows a library because it might feature iterators,
> clever error handling code, etc. and it might be tested better than
> yet annother quicky-hacky-implementation.
>
> are there any libraries or prominent applications known?
> thanks for response,

The basic idiom is so simple (two lines, see my last posting) that it
doesn't make any sense to package that into a lib. I don't know whether
your requirements are met by anthing done already. Did you check the RAA?
That's usually a good starting point.

http://raa.ruby...

Kind regards

robert