Ruby：不区分大小写的数组比较

Question

刚发现这个比较实际上是区分大小写的。任何人都知道一种不区分大小写的方法来完成同样的比较吗？

CardReferral.all.map(&:email) - CardSignup.all.map(&:email)

Answer 1

I don't think there is any "direct" way like the minus operator, but if you don't mind getting all your results in lowercase, you can do this:

CardReferral.all.map(&:email).map(&:downcase) - CardSignup.all.map(&:email).map(&:downcase)

Otherwise you'll have to manually do the comparison using find_all or reject :

signups = CardSignup.all.map(&:email).map(&:downcase)
referrals = CardReferral.all.map(&:email).reject { |e| signups.include?(e.downcase) }

I'd suggest that reading a reference of Ruby's standard types might help you come up with code like this. For example, "Programming Ruby 1.9" has all methods of the Enumerable object explained starting on page 487 ( find_all is on page 489).