def GAP(pred, conf, true):
    x = pd.DataFrame({'pred': pred, 'conf': conf, 'true': true})
    x.sort_values('conf', ascending=False, inplace=True, na_position='last')
    x['correct'] = (x.true == x.pred).astype(int)
    x['prec_k'] = x.correct.cumsum() / (np.arange(len(x)) + 1)
    x['term'] = x.prec_k * x.correct
    gap = x.term.sum() / x.true.count()

    return gap

model.compile(loss='my_loss',metrics=[GAP])