dataset.rb

  # Excel column string to 0 indexed position
  def self.excel_col_to_index(str)
    offset = 'A'.ord - 1
    str.upcase.chars.inject(0) { |x,c| x * 26 + c.ord - offset } - 1
  end

  # 0 based index to column letter
  def self.index_to_excel_col(index)
    'A'.tap do |name|
      index.times { name.succ! }
    end
  end