How to make a[2][2][3]=4 work?


#1

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

p a[1]=1

a[2][1]=2
#a[2][2][3]=4
p a


#2

I know this can work,but I think it is suck
a=Hash.new{|h,k|
h[k]=Hash.new{|h,k|h[k]=Hash.new{|h,k|h[k]={}}}
}

p a[1]=1

a[2][1]=2
a[2][2][3]=4
a[3][1][1][1]=1
p a


#3

p a
build_hash = proc {|h,k|h[k] = Hash.new &build_hash }
a = Hash.new &build_hash


#4

def recursive_hash
Hash.new { |h, k| h[k] = recursive_hash }
end
a = recursive_hash

Or even

class Hash
def self.recursive
new { |h, k| h[k] = recursive }
end
end

which gives

a = Hash.recursive
=>

a[1][2][3][4] = 1
=> 1

puts a.inspect
{1=>{2=>{3=>{4=>1}}}}


#5

In addition to what’s already been posted, there’s this, which doesn’t
require any extra variables or methods:

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

gz zz removed_email_address@domain.invalid writes:

a[2][1]=2
a[2][2][3]=4
a[3][1][1][1]=1
p a

irb(main):001:0> a = Hash.new{|h,k| h[k]=Hash.new &h.default_proc}
=> {}
irb(main):002:0> a[2][1]=2
=> 2
irb(main):003:0> a[2][2][3]=4
=> 4
irb(main):004:0> a[3][1][1][1]=1
=> 1
irb(main):005:0> p a
{2=>{1=>2, 2=>{3=>4}}, 3=>{1=>{1=>{1=>1}}}}
=> nil


#6

gz zz wrote:

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

p a[1]=1

a[2][1]=2
#a[2][2][3]=4
p a

Sure. Use Perl.

Oops, sorry. I forgot, datastructure autovivification is wrong,
variables springing into life (or maybe not, read the rest of the method
to find out) inadvertently are good.

Jenda


#7

On Jun 12, 6:21 am, Daniel M. removed_email_address@domain.invalid wrote:

In addition to what’s already been posted, there’s this, which doesn’t
require any extra variables or methods:

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

Thanks for this - I didn’t know about the default_proc method. Quite
elegant in this case.


#8

On 6/12/07, Jenda K. removed_email_address@domain.invalid wrote:

Sure. Use Perl.

Oops, sorry. I forgot, datastructure autovivification is wrong,
variables springing into life (or maybe not, read the rest of the method
to find out) inadvertently are good.

That’s okay, it happens to the best of us.

martin


#9

Sure. Use Perl.

What’s the ruby-way of such things?

e.g.:

int[eth0][ip] = “10.0.0.1”
int[eth0][mask] = “255.255.255.0”
int[eth0][cidr] = “24”
int[eth1][ip] = “10.0.1.1”
int[eth1][mask] = “255.255.255.0”
int[eth1][cidr] = “24”
.
.
.

I like it if I have all these informations handy within one hash. But
even for me as a realy ruby-newby this looks much more like perl than
ruby.

It would be great to hear your thoughts how this would be done “the ruby
way”…

clean and elegant :slight_smile:

–fsormok


#10

On Jun 12, 1:29 am, gz zz removed_email_address@domain.invalid wrote:

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

}

p a[1]=1

a[2][1]=2
#a[2][2][3]=4

a = {}
==>{}
a[1] = 1
==>1
a[ [2,1] ] = 2
==>2
a[ [2,2,3] ] = 4
==>4
p a
{[2, 2, 3]=>4, [2, 1]=>2, 1=>1}
==>nil


#11

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

irb(main):026:0> require ‘ostruct’
irb(main):027:0> int = Hash.new{|h,k| h[k]=OpenStruct.new}

a = {}
==>{}
a[1] = 1
==>1
a[ [2,1] ] = 2
==>2
a[ [2,2,3] ] = 4
==>4
p a
{[2, 2, 3]=>4, [2, 1]=>2, 1=>1}
==>nil

Tanks for the replies.

I’m just a little bit confused because in ruby everything is lean and
clean but when it comes to hashes of hashes it gets kind of complicated.
For me it looks like ruby has another “concept” of solving such things.

-fsormok


#12

On 7/23/07, Fsormok F. removed_email_address@domain.invalid wrote:

==>2
For me it looks like ruby has another “concept” of solving such things.

Hmm the context of this statement seems not complete in this thread,
maybe you could elaborate on this a little bit?
Personally I feel that Ruby’s concept of Hashes is clearcut and
exactly the same as in most of its relatives (Perl,Python…).

What exactly would you like to have “simpler”?

Cheers
Robert


#13

From: “Fsormok F.” removed_email_address@domain.invalid

int[eth1][ip] = “10.0.1.1”
It would be great to hear your thoughts how this would be done “the ruby
way”…

clean and elegant :slight_smile:

You can do that in Ruby, if you want to.
See: http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/255313

irb(main):011:0> int = Hash.new{|h,k| h[k]=Hash.new &h.default_proc}
=> {}
irb(main):012:0> int[:eth0][:ip] = “10.0.0.1”
irb(main):013:0> int[:eth0][:mask] = “255.255.255.0”
irb(main):014:0> int[:eth0][:cidr] = “24”
irb(main):015:0> int[:eth1][:ip] = “10.0.1.1”
irb(main):016:0> int[:eth1][:mask] = “255.255.255.0”
irb(main):017:0> int[:eth1][:cidr] = “24”
irb(main):018:0> int
=> {:eth0=>{:ip=>“10.0.0.1”, :mask=>“255.255.255.0”, :cidr=>“24”},
:eth1=>{:ip=>“10.0.1.1”, :mask=>“255.255.255.0”, :cidr=>“24”}}

Another possibility might be OpenStruct.

irb(main):026:0> require ‘ostruct’
=> true
irb(main):027:0> int = Hash.new{|h,k| h[k]=OpenStruct.new}
=> {}
irb(main):028:0> int[:eth0].ip = “10.0.0.1”
irb(main):029:0> int[:eth0].mask = “255.255.255.0”
irb(main):030:0> int[:eth0].cidr = “24”
irb(main):031:0> int[:eth1].ip = “10.0.1.1”
irb(main):032:0> int[:eth1].mask = “255.255.255.0”
irb(main):033:0> int[:eth1].cidr = “24”
irb(main):034:0> int
=> {:eth0=>#<OpenStruct ip=“10.0.0.1”, mask=“255.255.255.0”, cidr=“24”>,
:eth1=>#<OpenStruct ip=“10.0.1.1”, mask=“255.255.255.0”,
cidr=“24”>}

Regards,

Bill


#14

Thanx Mark

This is exactly what i liked to hear :slight_smile:

In my personal opinion, multilevel hashes aren’t clean and elegant in
any language.

HoH are quiet common in perl (at least I use them alot), not in Ruby
IMHO.

But as always: TMTOWTDI

I’d try to make an object out of it:

class Interface
attr_accessor :name, :ip, :mask, :cidr
end

i = Interface.new
i.name = “eth0”
i.ip = “10.0.0.1”
i.mask = “255.255.255.0”
i.cidr = 24

  • Mark.

#15

On Jul 20, 1:57 pm, Fsormok F. removed_email_address@domain.invalid wrote:

int[eth1][mask] = “255.255.255.0”
way"…

clean and elegant :slight_smile:

In my personal opinion, multilevel hashes aren’t clean and elegant in
any language. I’d try to make an object out of it:

class Interface
attr_accessor :name, :ip, :mask, :cidr
end

i = Interface.new
i.name = “eth0”
i.ip = “10.0.0.1”
i.mask = “255.255.255.0”
i.cidr = 24

  • Mark.

#16

2007/7/23, Fsormok F. removed_email_address@domain.invalid:

==>2
For me it looks like ruby has another “concept” of solving such things.
Its this what you are looking for?

$ ruby <<XXX

miss = lambda {|h,k| h[k] = Hash.new(&miss)}
hash = Hash.new(&miss)
hash[1][2]=3
hash[4]=5
p hash
XXX
{1=>{2=>3}, 4=>5}

Kind regards

robert


#17

Daniel M. wrote:

In addition to what’s already been posted, there’s this, which doesn’t
require any extra variables or methods:

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

That’s clever, but I think the way it automatically creates keys is
wrong. You need to be able to check to see if a key exists without
polluting the hash with a bunch of empties.

Hence my new gem:

http://github.com/dasil003/safe-nested-hash