pivot_table.rb

class PivotTable
  attr_accessor :table, :totals, :grand_total, :pivot_values
  
  def initialize(options)
    @data = options[:data]
    @row_fields = options[:row_fields].to_a
    @data_field = options[:data_field]
    @pivot_field = options[:pivot_field]
    @pivot_values = options[:pivot_values]
    
    build_table
  end
  
  private
  
  def build_table()
    @table = []
    @totals = {}
    @grand_total = 0
    
    @data.group_by {|r| @row_fields.map {|m| r.send(m)} }.each do |g, r|
      h = {}
      @row_fields.each_with_index { |field, i| h[field] = g[i] }
      total = 0
      vals = {}
      @pivot_values.each do |v|
        sum = r.
          select { |t| t.send(@pivot_field) == v }.
          map { |t| t.send(@data_field) }.
          reduce(0) { |s, n| s + n.to_f }
        
        h["#{@pivot_field}_#{clean v}"] = sum
        vals[v] = sum
        @totals[v] ||= 0
        @totals[v] += sum || 0
        @grand_total += sum || 0
        total += sum || 0
      end
      h[@pivot_field.to_s.pluralize] = vals
      h["sum_#{@data_field}"] = total
      @table << OpenStruct.new(h)
    end
  end
  
  def clean(s)
    s.to_s.gsub(/[,.| -]/, '_').gsub(/__+/, '_')
  end
end