def computeAverageRatings(self):
        """Compute average rating for each user"""
        self.userAvgRatings = {}
        for user in self.data:
            total = 0
            n = len(self.data)
            for value in self.data[user].values():
                total += value
            self.userAvgRatings[user] = total / n

    def flip(self):
        """flip self.data so {user: {band: rating} ...
        becomes
        {band: {user: rating} ...
        results will be in self.flippedData
        """
        self.flippedData = {}
        for (user, ratings) in self.data.items():
            for (band, rating) in ratings.items():
                if band in self.flippedData:
                    bandratings = self.flippedData[band]
                else:
                    bandratings = {}
                bandratings[user] = rating
                self.flippedData[band] = bandratings