生成另外一列，计算最近六天内“m7-2”这一列小于0的个数。
trade_date m7-2
20211110 -0.01980
20211109 0.00300
20211108 -0.00031
20211105 0.00195
20211104 0.00849
20211103 -0.01024
20211102 0.00052
20211101 0.02188
20211029 0.00247
20211028 0.00202
20211027 -0.00528
20211026 -0.00907
20211025 0.00638
20211022 -0.02157
20211021 -0.00206
20211020 0.00099
20211019 -0.00278
20211018 -0.00601
20211015 0.01241
20211014 0.00489
20211013 0.03406
20211012 -0.00593
20211011 0.00681
20211008 0.00916
20210930 -0.00107
20210929 -0.00146
20210928 0.00948
20210927 -0.01459
20210924 -0.00475
20210923 -0.00979
20210922 -0.00349
20210917 -0.01116
20210916 -0.00467
20210915 -0.01210
20210914 0.01311
20210913 0.00556
20210910 0.01759
20210909 0.00092
20210908 0.00638
20210907 -0.02568
20210906 -0.00083
20210903 -0.00538
20210902 -0.00068
20210901 -0.02328
20210831 -0.01940
20210830 0.00817
20210827 0.02965
20210826 0.00819
20210825 0.00459
20210824 0.01188
20210823 0.00567
20210820 0.00138
20210819 0.00507
20210818 -0.00284
20210817 -0.00209
20210816 0.00335
20210813 -0.00638
20210812 0.00947
20210811 -0.00566
20210810 -0.01757
20210809 -0.02017
20210806 -0.00051
20210805 -0.00845
20210804 -0.00465
20210803 -0.00222
20210802 0.00984
最近6天，你就肉眼观察法呗