From: Joel VanderWerf <vjoel@...>
Date: 2004-08-14T05:46:26+09:00
Subject: Re: Question: A method for summing several variables

Harry Truax wrote:
> We initially set all boxes to '' as in this example:
> 
> box1_1 = '' box1_2 = '' . . box12_1 = '' box12_2 = '' etc. . .
> 
> How can I add up a range of boxes without having to specifiy each box
> by name? Maybe a nice short method I could call, giving it the
> starting box and the step value (sometimes the box numbers differ by
> a value other than 1, like my example above where they differ by 2)
> and the number of boxes to add.
> 
> Below is a method I tried, but 'box' was not being properly handled -
> box could be say, 'box1_10', but I want the value that 'box1_10'
> points to, not the .to_f value of the string 'box1_10'.

Destructive string methods are your best friends in this case: replace, 
sub!, gsub!, tr!, etc. As long as you use them, you are operating on the 
value that box1_10 points to. For example:

   $SAFE = 3

   boxes = Array.new(10) {Array.new(10)}

   boxes[2][4] = box2_4 = ''

   box2_4.replace "1.23"
   p boxes[2][4]        # ==> "1.23"

   boxes[2][4].gsub!(/\d/, "#")
   p box2_4             # ==> "#.##"

   boxes[2][4].replace "3.45"
   p box2_4             # ==> "3.45"

And now you can get fancy to make life easier:

   class Table2D_StringCodedFloats # ok, choose a better name
     def initialize(boxes)
       @boxes = boxes
     end

     def [](i,j)
       @boxes[i][j].to_f
     end

     def []=(i,j, val)
       @boxes[i][j].replace val.to_s
     end
   end

   table = Table2D_StringCodedFloats.new(boxes)

   p table[2,4]      # ==> 3.45
   table[2,4] = 7
   p table[2,4]      # ==> 7.0

   p box2_4          # ==> "7"
   table[2,4] += 1
   p box2_4          # ==> "8.0"

And now you can iterate through the boxes just by using integers in 
table[i,j]:

   10.times do |i|
     10.times do |j|
      table[i,j] = i+j
     end
   end

   p box2_4          # ==> "6"

What the heck, let's make it Enumerable:

   class Table2D_StringCodedFloats
     include Enumerable

     def each
       @boxes.each_with_index do |row, i|
         row.each_with_index do |value, j|
           yield i,j,value.to_f
         end
       end
     end
   end

   p table.select {|i,j,value| value > 16}
     # ==> [[8, 9, 17.0], [9, 8, 17.0], [9, 9, 18.0]]