Refactoring blog: Parameterization

parameterized-1.rb

def weight_avg_gross_profit(reports)
  # find total weight, sum of sale_revenue
  total_weight = reports.reduce(0) { |sum, r| sum + r.sale_revenue }

  # find sum products
  sum_prod = reports.reduce do |sum, r|
    sum + (r.percent_gross_profit * r.sale_revenue)
  end
  
  # simple weight average formula, (w1*x1 + w2*x2) / (w1 + w2)
  sum_prod / total_weight
end