subtract.rb

README.md

This is like a-b, where a and b are sets, but it effectively uses a case-insensitive comparison function.

The reason for this is that Rails/MySQL find_by is case-insensitive. So if you have a data feed where someone's changed only the case, but don't want that to actually affect anything, you can use this function to see if there's a real difference (beyond just flipping the case).

gistfile1.txt

def case_insensitive_subtract(a,b)

  a_items_by_lowercase = {}
  a.each { |item| a_items_by_lowercase[item.downcase] = item }
  b_items_by_lowercase = {}
  b.each { |item| b_items_by_lowercase[item.downcase] = item }

  lowercase_diff = a_items_by_lowercase.keys - b_items_by_lowercase.keys
  result = Set.new
  lowercase_diff.each { |lowercase| result.add a_items_by_lowercase[lowercase] }

end