Find duplicates in MongoDB collection using Aggregate in Rails Console

find_duplicates.rb

results = Merchant.collection.aggregate([
  { "$group" => { 
    _id: { "confirmation_token" => "$confirmation_token"}, 
    recordIds: {"$addToSet" => "$_id" },
    count: { "$sum" => 1 } 
  }}, 
  { "$match" => { 
    count: { "$gt" => 1 } 
  }}
])