tricky hash initialization

[Ray Pereda]

h = Hash.new {|h,k| h[k] = {} }

This is one level deep defaults to a fresh new hash.

h = Hash.new {|h,k| h[k] = Hash.new{ |h2,k2| h2[k2] = {} } }

This is two levels deep initialization to a fresh new hash.

How do I this for arbitrarily deep hashes?

h["a"]["b"]["c"] = 3 #=> {"c"=>3}

I'm using this to build very clean implementations of state machine
building algorithms.

Your help is very much appreciated.

-Ray

 

[Sebastian Hungerecker]

How do I this for arbitrarily deep hashes?

Hash.new {|h,k| h[k] = Hash.new(&h.default_proc)}

HTH,
Sebastian

 

[Ray Pereda]

Hash.new {|h,k| h[k] = Hash.new(&h.default_proc)}

Thanks for the attempt. Seems on the right track but not quite.

h = Hash.new {|h,k| h[k] = Hash.new(&h.default_proc)} => {}
h["a"]["b"]["c"] => {}
h

=> {"c"=>{}}

After h["a"]["b"]["c"]
what needs to happen is h is equal to
{"a"=>{"b"=>{"c"=>{}}}}

Appreciating the Ruby Community's Help,
Ray

 

[Mikael Høilund]

h =3D Hash.new {|h,k| h[k] =3D Hash.new(&h.default_proc)}

Don't do that. The h inside the block is conflicting with the h =20
outside. Make sure the variables don't collide, and it works:

the_hash =3D Hash.new {|h,k| h[k] =3D Hash.new(&h.default_proc)} =3D> {}
the_hash[:a][:b][:c] =3D> {}
the_hash

=3D> {:a=3D>{:b=3D>{:c=3D>{}}}}

--=20
Mikael H=F8ilund
http://hoilund.org/

 

[David A. Black]

Hi --

Hash.new {|h,k| h[k] = Hash.new(&h.default_proc)}

Thanks for the attempt. Seems on the right track but not quite.

h = Hash.new {|h,k| h[k] = Hash.new(&h.default_proc)} => {}
h["a"]["b"]["c"] => {}
h

=> {"c"=>{}}

After h["a"]["b"]["c"]
what needs to happen is h is equal to
{"a"=>{"b"=>{"c"=>{}}}}

I think it's a variable clobbering issue. Try this:

hash = Hash.new {|h,k| h[k] = Hash.new(&h.default_proc) }


David

 

[David A. Black]

I should add: the same-variable-name version works in Ruby 1.9.


David

Hi --

Hash.new {|h,k| h[k] = Hash.new(&h.default_proc)}

Thanks for the attempt. Seems on the right track but not quite.

h = Hash.new {|h,k| h[k] = Hash.new(&h.default_proc)} => {}
h["a"]["b"]["c"] => {}
h

=> {"c"=>{}}

After h["a"]["b"]["c"]
what needs to happen is h is equal to
{"a"=>{"b"=>{"c"=>{}}}}

I think it's a variable clobbering issue. Try this:

hash = Hash.new {|h,k| h[k] = Hash.new(&h.default_proc) }


David

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