table_dittoize.rb

require 'cucumber'
require 'cucumber/ast/table'

def dittoize(table)
  rows = table.rows

  rows.each_cons(2) do |upper, lower|
    next unless lower.any? { |cell| cell == "''" }
    lower.each_with_index do |cell, idx|
      lower[idx] = upper[idx] if cell == "''"
    end
  end

  Cucumber::Ast::Table.new([table.headers] + rows)
end

raw = [["zip"], ["12345"], ["''"]]
t = Cucumber::Ast::Table.new(raw)
puts t
puts dittoize(t)

complex = [["zip",   "phone"], 
           ["12345", "3135551212"], 
           ["''",    "1234567890"], 
           ["54321", "''"],
           ["''",    "''"],
           ["''",    "123"]]
t = Cucumber::Ast::Table.new(complex)
puts t
puts dittoize(t)