From: Robert Klemme <shortcutter@...>
Date: 2009-04-20T20:02:32+09:00
Subject: Re: Hashed matrix

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 = 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

This should have read

raise ArgumentError, "Not a state %p" % val unless State === 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.rubybestpractices.com/
>



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