Rails rake task, clean up database, remove duplicates on multiple columns

# lib/tasks/people.rb
 task cleanup: :environment do
 # find all models and group them on keys which should be common
 grouped_by_first_last_name = Person.all.group_by{|model| [model.fname, model.lname] }
 grouped_by_email = Person.all.group_by{|model| [model.email] }
 grouped_by_first_last_name.merge(grouped_by_email).values.each do |duplicates|
 # first_one = duplicates.shift # keep the first one
 last_one = duplicates.pop # keep the last one
 # if there are any more left, they are duplicates
 # so delete all of them
 duplicates.each{ |double| double.destroy } # duplicates can now be destroyed
 end
 end

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