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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def round_robin(self, x, y, n_keep):
 """ Ensures all classes get representative features, not just those with strong features """

        vals = y.unique()
        scores = {}
        for cls in vals:
            scores[cls] = self.rank(x, np.equal(cls, y).astype('Int64'))
            scores[cls].reverse()
        keepers = set()
        while len(keepers) < n_keep:
            for cls in vals:
                keepers.add(scores[cls].pop()[1])
        return list(keepers)