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Hashed matrix

Yoann Moreau

4/20/2009 10:05:00 AM

Hello, I'd like to use a specific matrix with string as key for lines
and integer index for columns. I could also use string for columns (a
string version of integer), it doesn't matter. I use the matrix to store
a small object (named State) I just need to access data like that :
matrix[a_string][a_number]

Here is how I tried to do it :
matrix = Hash.new{ |hash, key| hash[key] = Array.new(5, State.new(0,
"")) }

But I have strange values, is there a better way to make that matrix ?
--
Posted via http://www.ruby-....
3 Answers

Robert Klemme

4/20/2009 11:02:00 AM

0

2009/4/20 Yoann Moreau <yoni612@hotmail.com>:
> Hello, I'd like to use a specific matrix with string as key for lines
> and integer index for columns. I could also use string for columns (a
> string version of integer), it doesn't matter. I use the matrix to store
> a small object (named State) I just need to access data like that :
> matrix[a_string][a_number]
>
> Here is how I tried to do it :
> matrix = Hash.new{ |hash, key| hash[key] = Array.new(5, State.new(0,
> "")) }

You want the block form of Array.new because otherwise all array
entries point to the same object:

matrix = Hash.new{ |hash, key| hash[key] = Array.new(5) { State.new(0,"") } }

Alternative approach: use an Array of String and Fixnum as Hash key:

class Matrix
def initialize
@hash = Hash.new {|h,k| h[k] = State.new(0, "")}
end

def [](row,col)
@hash[[row, col]]
end

def []=(row,col, val)
raise ArgumentError, "Not a state %p" % val
@hash[[row, col]] = val
end
end

This is likely more efficient if your matrices are large and sparse.

Kind regards

robert

--
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestprac...

Robert Klemme

4/20/2009 11:03:00 AM

0

2009/4/20 Robert Klemme <shortcutter@googlemail.com>:
> 2009/4/20 Yoann Moreau <yoni612@hotmail.com>:
>> Hello, I'd like to use a specific matrix with string as key for lines
>> and integer index for columns. I could also use string for columns (a
>> string version of integer), it doesn't matter. I use the matrix to store
>> a small object (named State) I just need to access data like that :
>> matrix[a_string][a_number]
>>
>> Here is how I tried to do it :
>> matrix =3D Hash.new{ |hash, key| hash[key] =3D Array.new(5, State.new(0,
>> "")) }
>
> You want the block form of Array.new because otherwise all array
> entries point to the same object:
>
> matrix =3D Hash.new{ |hash, key| hash[key] =3D Array.new(5) { State.new(0=
,"") } }
>
> Alternative approach: use an Array of String and Fixnum as Hash key:
>
> class Matrix
> =A0def initialize
> =A0 =A0@hash =3D Hash.new {|h,k| h[k] =3D State.new(0, "")}
> =A0end
>
> =A0def [](row,col)
> =A0 =A0@hash[[row, col]]
> =A0end
>
> =A0def []=3D(row,col, val)
> =A0 =A0raise ArgumentError, "Not a state %p" % val

This should have read

raise ArgumentError, "Not a state %p" % val unless State =3D=3D=3D val

> =A0 =A0@hash[[row, col]] =3D val
> =A0end
> end
>
> This is likely more efficient if your matrices are large and sparse.
>
> Kind regards
>
> robert
>
> --
> remember.guy do |as, often| as.you_can - without end
> http://blog.rubybestprac...
>



--=20
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestprac...

Yoann Moreau

4/20/2009 11:15:00 AM

0

Thanks for your answer, you're right I had the same object in my array,
this is why I had strange values.
I use a really small matrix so it's not a big deal to be efficient, I'll
use your first idea.

Thank you.
--
Posted via http://www.ruby-....