A helper to convert model arrays into crosstab reports

Crosstab for Ruby

# Crosstab module for ruby.  This class allows you to iterate through an
# array of models (rows) and refactor the data to a crosstab format.  
# This takes one of the columns and makes it your row-key, another column 
# and makes it column-keys, then sums all cell values where these two 
# keys interesect.
#
# Currently only a single column can be used for row-keys and column-keys 
# but this may be expanded in the future with the addition of 'row grouping'
 

class Crosstab
  # tab = Crosstab.new(Model.find(:all), :rows => 'region', :cols => 'site', :cells => 'value' )
  # TODO V2: tab = Crosstab.new(Model.find(:all), :rows => ['country', 'region'], :cols => 'site', :cells => 'value', :function => 'sum' )

   def initialize array, params
    @rows = params[:rows]
    @cols = params[:cols]
    @cells = params[:cells]
    @function = params[:function]

    @row_hash = {}
    @col_hash = {}
    
    vals = {}
    array.each { |obj|
      raise "Invalid row name, make sure your results have a column/member named '#{@rows}'" if obj[@rows].nil?
      row_key = "#{obj[@rows]}"
      col_key = "#{obj[@cols]}"
      value = obj[@cells]
      #puts "#{row_key}:#{col_key}=#{value}"
      @row_hash[row_key] = {} if !@row_hash.key?(row_key)
      @row_hash[row_key][col_key] = !@row_hash[row_key].key?(col_key) ? value : @row_hash[row_key][col_key] + value
      @col_hash[col_key] = true if !@col_hash.key?(col_key)
      #puts "Stored: #{@row_hash[row_key][col_key]}"
    }

  end

  def to_csv

    #puts "#{@col_hash.keys.length} columns and #{@row_hash.keys.length} rows"
    puts "Crosstab,#{@col_hash.keys.join(",")}"
    #puts @row_hash.keys.join(",")

    @row_hash.keys.each { |r|
      print "#{r}"
      @col_hash.keys.each {|c|
        print ",#{@row_hash[r][c]}"
      }
      puts ""
    }
  end

end