Preserve insert order in a Hash

ruby-talk
1

Hi,
I would like to know if it's possible to insert values in a Hash and
then extract all of them in the same insertion order.

I noticed that if I then try to print the content of an Hash using
"each" the order is not the same as the insertion.

Thanks

···

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2

# I would like to know if it's possible to insert values in a Hash and
# then extract all of them in the same insertion order.

only in ruby 1.9

C:\ruby1.9\bin>irb.bat

h={}

=> {}

h[1]=1

=> 1

h[2]=1

=> 1

h[3]=1

=> 1

h

=> {1=>1, 2=>1, 3=>1}

h[1.5]=1

=> 1

h

=> {1=>1, 2=>1, 3=>1, 1.5=>1}

h[0]=1

=> 1

h

=> {1=>1, 2=>1, 3=>1, 1.5=>1, 0=>1}

RUBY_VERSION

=> "1.9.0"

···

From: Me Me [mailto:emanuelef@tiscali.it]

3

gem install orderedhash

a @ http://codeforpeople.com/

···

On Sep 18, 2008, at 3:42 AM, Me Me wrote:

Hi,
I would like to know if it's possible to insert values in a Hash and
then extract all of them in the same insertion order.

I noticed that if I then try to print the content of an Hash using
"each" the order is not the same as the insertion.

Thanks
-- Posted via http://www.ruby-forum.com/\.

--
we can deny everything, except that we have the possibility of being better. simply reflect on that.
h.h. the 14th dalai lama

4

Peña, Botp wrote:

From: Me Me [mailto:emanuelef@tiscali.it]
# I would like to know if it's possible to insert values in a Hash and
# then extract all of them in the same insertion order.

only in ruby 1.9

Could anybody explain why this feature was added? Isn't it going to slow
down the operations on the Hash? I think it is useless to mix Array with
Hash.

TPR.

···

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5

If scale is needed this has been implemented by Takuma Ozawa as a very
efficient RB tree which I used on a Mac:

sudo gem install rbtree
irb
require 'rbtree'
a=RBTree.new
a['x']=1
a['z']=2
a['y']=3
a
============> #RBTree:{'x'=>1,'y'=>3,'z'=>2}

···

On Thu, Sep 18, 2008 at 11:47 AM, ara.t.howard <ara.t.howard@gmail.com>wrote:

On Sep 18, 2008, at 3:42 AM, Me Me wrote:

Hi,

I would like to know if it's possible to insert values in a Hash and
then extract all of them in the same insertion order.

I noticed that if I then try to print the content of an Hash using
"each" the order is not the same as the insertion.

Thanks
-- Posted via http://www.ruby-forum.com/\.

gem install orderedhash

a @ http://codeforpeople.com/
--
we can deny everything, except that we have the possibility of being
better. simply reflect on that.
h.h. the 14th dalai lama

6

Peña, Botp wrote:

From: Me Me [mailto:emanuelef@tiscali.it]
# I would like to know if it's possible to insert values in a Hash and
# then extract all of them in the same insertion order.

only in ruby 1.9

Well, that is not *entirely* true.

h={}
p h
h[1]=1
p h
h[2]=1
p h
h[3]=1
p h
h
p h
h[1.5]=1
p h
h
p h
h[0]=1
p h
h
p h

yields:

{}
{1=>1}
{1=>1, 2=>1}
{1=>1, 2=>1, 3=>1}
{1=>1, 2=>1, 3=>1}
{1=>1, 2=>1, 3=>1, 1.5=>1}
{1=>1, 2=>1, 3=>1, 1.5=>1}
{1=>1, 2=>1, 3=>1, 1.5=>1, 0=>1}
{1=>1, 2=>1, 3=>1, 1.5=>1, 0=>1}

in JRUBY 1.1 which I am running on windows under netbeans.

···

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7

Thomas B. wrote:

Peña, Botp wrote:

From: Me Me [mailto:emanuelef@tiscali.it]
# I would like to know if it's possible to insert values in a Hash and
# then extract all of them in the same insertion order.

only in ruby 1.9

Could anybody explain why this feature was added? Isn't it going to slow
down the operations on the Hash? I think it is useless to mix Array with
Hash.

TPR.

well, basically I just need a Hash to use String as indexes like

sourceInfo = Hash.new
sourceInfo["var1"]=123
sourceInfo["var2"]=2
sourceInfo["var3"]=3
sourceInfo["var4"]=23

and then print them in the exact order of insertion

···

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8

Hi,

Could anybody explain why this feature was added?

Useful for some cases, especially for keyword arguments.

Isn't it going to slow down the operations on the Hash?

No. hash reference operation does not touch order information, only
for iteration. Memory consumption increased a bit.

              matz.

···

In message "Re: Preserve insert order in a Hash" on Thu, 18 Sep 2008 18:54:20 +0900, "Thomas B." <tpreal@gmail.com> writes:

9

cfp:~ > cat a.rb
require 'rubygems'
require 'rbtree'

# rbtree is sorted by the keys 'natural' sort order
# *not* the insertion order

rb = RBTree.new

rb['z'] = 3
rb['y'] = 2
rb['x'] = 1

rb.each do |key, value|
   puts "#{ key } : #{ value }"
end

cfp:~ > ruby a.rb
x : 1
y : 2
z : 3

a @ http://codeforpeople.com/

···

On Sep 18, 2008, at 10:01 AM, jim finucane wrote:

If scale is needed this has been implemented by Takuma Ozawa as a very
efficient RB tree which I used on a Mac:

sudo gem install rbtree
irb
require 'rbtree'
a=RBTree.new
a['x']=1
a['z']=2
a['y']=3
a

--
we can deny everything, except that we have the possibility of being better. simply reflect on that.
h.h. the 14th dalai lama

10

Can't you just sort them on the way out?
i.e.

sourceinfo.keys.sort.each { |k|
  sourceinfo[k].do_stuff
}

···

On Thu, Sep 18, 2008 at 11:13 AM, Me Me <emanuelef@tiscali.it> wrote:

Thomas B. wrote:

Peña, Botp wrote:

From: Me Me [mailto:emanuelef@tiscali.it]
# I would like to know if it's possible to insert values in a Hash and
# then extract all of them in the same insertion order.

only in ruby 1.9

Could anybody explain why this feature was added? Isn't it going to slow
down the operations on the Hash? I think it is useless to mix Array with
Hash.

TPR.

well, basically I just need a Hash to use String as indexes like

sourceInfo = Hash.new
sourceInfo["var1"]=123
sourceInfo["var2"]=2
sourceInfo["var3"]=3
sourceInfo["var4"]=23

and then print them in the exact order of insertion

--
Rasputnik :: Jack of All Trades - Master of Nuns
http://number9.hellooperator.net/

11

a = []
a.push 1
a.push 2
a.push 3
a.each {|e|puts e}

12

well, basically I just need a Hash to use String as indexes like

sourceInfo = Hash.new
sourceInfo["var1"]=123
sourceInfo["var2"]=2
sourceInfo["var3"]=3
sourceInfo["var4"]=23

What do you want to happen if sourceInfo["var2"] is assigned a second
time? Do you want to replace it where it originally was in the sequence,
or do you want to delete it and add the new value to the end? Or do you
want both elements to appear at the same time? Or doesn't it matter?

I am just wondering because perhaps all you need is

sourceInfo =
sourceInfo << ["var1",123]
sourceInfo << ["var2",2]
sourceInfo << ["var3",3]
sourceInfo << ["var4",4]
sourceInfo.each { |k,v| puts "#{k}=>#{v}" }

At least, that's fine if all you want to do is iterate over the
collection and add new elements. Finding or deleting elements by key
requires a linear search:

dummy,value = sourceInfo.find { |k,v| k == "var2" }

However you can optimise this by building a hash as you go which points
to the same elements; or you could build an array containing just the
keys.

  class HashAndArray
    def initialize
      @h, @a = {},
    end
    def (k)
      @h[k]
    end
    def =(k,v)
      @a << k unless @h.has_key?(k)
      @h[k] = v
    end
    def each
      @a.each { |k| yield k,@h[k] }
    end
  end

  sourceInfo = HashAndArray.new
  sourceInfo["var1"]=123
  sourceInfo["var2"]=2
  sourceInfo["var3"]=3
  sourceInfo["var4"]=23
  sourceInfo.each { |k,v| puts "#{k}=>#{v}" }
  puts sourceInfo["var2"]

Adding a delete() method is left as an exercise.

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13

If I remember correctly, it's been a while since I looked at the code, 1.9
implements this by using a singly linked list which introduces a small
overhead only when elements are either added or deleted.

···

On Thu, Sep 18, 2008 at 6:28 AM, Yukihiro Matsumoto <matz@ruby-lang.org>wrote:

Hi,

In message "Re: Preserve insert order in a Hash" > on Thu, 18 Sep 2008 18:54:20 +0900, "Thomas B." <tpreal@gmail.com> > writes:

>Could anybody explain why this feature was added?

Useful for some cases, especially for keyword arguments.

>Isn't it going to slow down the operations on the Hash?

No. hash reference operation does not touch order information, only
for iteration. Memory consumption increased a bit.

--
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denhaven2.com/

14

Hi,

Yukihiro Matsumoto wrote in [ruby-talk:315237]:
At Thu, 18 Sep 2008 19:28:28 +0900,

>Could anybody explain why this feature was added?

Useful for some cases, especially for keyword arguments.

And the performance of iterations improved a little, but
significantly.

···

--
Nobu Nakada

15

Dick Davies wrote:

···

On Thu, Sep 18, 2008 at 11:13 AM, Me Me <emanuelef@tiscali.it> wrote:

Hash.

and then print them in the exact order of insertion

Can't you just sort them on the way out?
i.e.

sourceinfo.keys.sort.each { |k|
  sourceinfo[k].do_stuff
}

thanks
well in this case they will be sorted alphabetically, right?
the example is simplyfied, in my case the keys have differernt names.
--
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16

unknown wrote:

a =
a.push 1
a.push 2
a.push 3
a.each {|e|puts e}

I think this is not my case, I need a Hash as I explained

···

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17

Hi,

···

In message "Re: Preserve insert order in a Hash" on Thu, 18 Sep 2008 21:44:23 +0900, "Rick DeNatale" <rick.denatale@gmail.com> writes:

No. hash reference operation does not touch order information, only
for iteration. Memory consumption increased a bit.

If I remember correctly, it's been a while since I looked at the code, 1.9
implements this by using a singly linked list which introduces a small
overhead only when elements are either added or deleted.

You're right. Thank you for pointing out.

              matz.

18

FWIW, Ruby 1.9 seems to keep the original insertion order, reassiging a
value to an existing key leaves the order unchanged:

$ irb1.9
irb(main):001:0> a = {a: 1, b: 2, c: 3}
=> {:a=>1, :b=>2, :c=>3}
irb(main):002:0> a.keys
=> [:a, :b, :c]
irb(main):003:0> a[:b] = 4
=> 4
irb(main):004:0> a.keys
=> [:a, :b, :c]
irb(main):005:0> a
=> {:a=>1, :b=>4, :c=>3}
irb(main):006:0>

At least my somewhat out of date 1.9 does

$ ruby1.9 -v
ruby 1.9.0 (2008-03-21 revision 0) [i686-darwin9.2.2]

···

On Thu, Sep 18, 2008 at 8:42 AM, Brian Candler <b.candler@pobox.com> wrote:

> well, basically I just need a Hash to use String as indexes like
>
> sourceInfo = Hash.new
> sourceInfo["var1"]=123
> sourceInfo["var2"]=2
> sourceInfo["var3"]=3
> sourceInfo["var4"]=23

What do you want to happen if sourceInfo["var2"] is assigned a second
time? Do you want to replace it where it originally was in the sequence,
or do you want to delete it and add the new value to the end? Or do you
want both elements to appear at the same time? Or doesn't it matter?

--
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denhaven2.com/

19

I think this is not my case, I need a Hash as I explained

Here's an implementation for ruby 1.8 ... I apologize for the lack of tests.

class InsertOrderPreservingHash
  include Enumerable
    def initialize(*args, &block)
    @h = Hash.new(*args, &block)
    @ordered_keys =
  end
    def =(key, val)
    @ordered_keys << key unless @h.has_key? key
    @h[key] = val
  end

  def each
    @ordered_keys.each {|k| yield(k, @h[k])}
  end
  alias :each_pair :each
    def each_value
    @ordered_keys.each {|k| yield(@h[k])}
  end

  def each_key
    @ordered_keys.each {|k| yield k}
  end
    def keys
    @ordered_keys
  end
    def values
    @ordered_keys.map {|k| @h[k]}
  end
    def clear
    @ordered_keys.clear
    @h.clear
  end
    def delete(k, &block)
    @ordered_keys.delete k
    @h.delete(k, &block)
  end

  def reject!
    del =
    each_pair {|k,v| del << k if yield k,v}
    del.each {|k| delete k}
    del.empty? ? nil : self
  end

  def delete_if(&block)
    reject!(&block)
    self
  end
    %w(merge!).each do |name|
    define_method(name) do |*args|
      raise NotImplementedError, "#{name} not implemented"
    end
  end

  def method_missing(*args)
    @h.send(*args)
  end
end

# example:

h = InsertOrderPreservingHash.new

h[:aaa] = 0
h[:foo] = 123
h[:bar] = 456
h[:baz] = 789
h.delete :aaa
h[:aaa] = 1

h.each_pair {|k,v| p [k,v]}

# produces:

[:foo, 123]
[:bar, 456]
[:baz, 789]
[:aaa, 1]

Regards,

Bill

···

From: "Me Me" <emanuelef@tiscali.it>

20

Bill Kelly wrote:

From: "Me Me" <emanuelef@tiscali.it>

I think this is not my case, I need a Hash as I explained

Here's an implementation for ruby 1.8 ... I apologize for the lack of
tests.

Thanks a lot! That worked perfectly
Bye

···

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