habitica/migrations/20131117_remove_undefined_pets.js

// once and for all!

db.users.find({'items.pets':{$exists:1}},{'items.pets':1}).forEach(function(user){
  _.reduce(user.items.pets, function(m,v,k){
    if (!k.indexOf('undefined')) m.push(k);
    return m;
  }, []).forEach(function(key){
    delete user.items.pets[key];
  })

  db.users.update({_id:user._id}, { $set:{'items.pets':user.items.pets} });
});