From: Jim Carter <jcarter@...>
Date: 2011-02-03T05:22:37+09:00
Subject: Re: Returning a column vector from a 2D array

Using Matrix.rb does not work in this application, because I have to
assign matrix values dynamically, and it appears that Matrix class
requires static assignment of the matrix.  That's why I created my own
Array2D class.  I was able to take and modify a method from Matrix.rb to
solve this problem however.  It is the column method (see below)

class Array2D

  require 'matrix'

  def initialize(row, column)   #this creates the 2D array structure
      @data = Array.new(row) { Array.new(column) {0}}   #initialize
array with
                                                        #0's
  end

  def [](x, y)    #this allows one read access

    # to cells within 2D array
      @data[x][y]
  end

  def []=(x, y, value)  #this allows one write access to cells within 2D
array
     @data[x][y] = value
  end

  #
  # Returns column vector number +j+ of the matrix as a Vector (starting
at 0
  # like an array).  When a block is given, the elements of that vector
are
  # iterated.
  #
  def column(j,row_size) # :yield: e
    if block_given?
      row_size.times do |i|
        yield @data[i][j]
      end
    else
      col = (0 ... row_size).collect {|i|
        @data[i][j]
      }
    #Vector.elements(col, false)
    end
  end #column


end

This is the call

 puts ary_length = @index
 puts @data_array.column(0,ary_length)

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