由于数据出现错误
DataError: No numeric types to aggregate
改正以后才认识到astype的重要性。
Top15[‘populations‘] = Top15[‘Energy Supply‘].div(Top15[‘Energy Supply per Capita‘]).astype(float) df_mean = ((df.set_index(‘Continent‘).groupby(level=0)[‘populations‘].agg({‘mean‘ : np.mean}))) #加了astype(float)后无错误
原文：https://www.cnblogs.com/Shinered/p/9242597.html