為什么日期格式會隨np.where發生變化以及如何阻止它發生

我有來自資料幀的以下資料子集。

{'NID': {131598: '215026851',
  131599: '215026851',
  131600: '215026851',
  131601: '215026851',
  131602: '215026851',
  131603: '215026851',
  131604: '215026851',
  131605: '215026851',
  131606: '215026851'},
 'AbCode': {131598: 0,
  131599: 0,
  131600: 0,
  131601: 0,
  131602: 0,
  131603: 1,
  131604: 0,
  131605: 0,
  131606: 0},
 'ABdat': {131598: Timestamp('2018-01-24 00:00:00'),
  131599: Timestamp('2019-01-25 00:00:00'),
  131600: NaT,
  131601: Timestamp('2019-11-08 00:00:00'),
  131602: Timestamp('2020-01-24 00:00:00'),
  131603: Timestamp('2020-02-15 00:00:00'),
  131604: Timestamp('2020-10-16 00:00:00'),
  131605: Timestamp('2020-10-26 00:00:00'),
  131606: NaT}}

格式化后的資料如下所示

          NID     AbCode  ABdat
131598  215026851   0   2018-01-24
131599  215026851   0   2019-01-25
131600  215026851   0   NaT
131601  215026851   0   2019-11-08
131602  215026851   0   2020-01-24
131603  215026851   1   2020-02-15
131604  215026851   0   2020-10-16
131605  215026851   0   2020-10-26
131606  215026851   0   NaT 

對于 AbCode = 0，我想用缺失 (NaT) 替換 ABdat，對于 AbCode = 1，我想用 ABdat-7days 替換 ABdat

我在下面撰寫了以下 np.where 代碼來執行此操作。

breed_info['ABdat'] = np.where(breed_info.AbCode == 1, breed_info['ABdat'] - pd.DateOffset(days=7), breed_info['ABdat'].isnull)

輸出如下所示

          NID   AbCode       ABdat
131598  215026851   0   <bound method Series.isnull of 49017 ...
131599  215026851   0   <bound method Series.isnull of 49017 ...
131600  215026851   0   <bound method Series.isnull of 49017 ...
131601  215026851   0   <bound method Series.isnull of 49017 ...
131602  215026851   0   <bound method Series.isnull of 49017 ...
131603  215026851   1   1581120000000000000
131604  215026851   0   <bound method Series.isnull of 49017 ...
131605  215026851   0   <bound method Series.isnull of 49017 ...
131606  215026851   0   <bound method Series.isnull of 49017 ...

您能否告知為什么日期格式會發生變化以及如何避免這種情況發生？

謝謝

uj5u.com熱心網友回復：

最簡單的是使用帶有熊貓方法的一些熊貓解決方案，例如Series.where：

breed_info['ABdat'] = (breed_info['ABdat'] - pd.DateOffset(days=7))
                                                        .where(breed_info.AbCode == 1)

使用np.where帶有助手的 hacky 解決方案Series：

breed_info['ABdat'] = np.where(breed_info.AbCode == 1,
                               breed_info['ABdat'] - pd.DateOffset(days=7),
                                pd.Series(pd.NaT, index=breed_info.index))
print (breed_info)
              NID  AbCode      ABdat
131598  215026851       0        NaT
131599  215026851       0        NaT
131600  215026851       0        NaT
131601  215026851       0        NaT
131602  215026851       0        NaT
131603  215026851       1 2020-02-08
131604  215026851       0        NaT
131605  215026851       0        NaT
131606  215026851       0        NaT

因為如果傳遞pd.NAT它回傳下劃線 numpy 陣列（以納秒為單位）：

breed_info['ABdat'] = np.where(breed_info.AbCode == 1, 
                               breed_info['ABdat'] - pd.DateOffset(days=7),
                               pd.NaT)
print (breed_info)
              NID  AbCode                ABdat
131598  215026851       0                  NaT
131599  215026851       0                  NaT
131600  215026851       0                  NaT
131601  215026851       0                  NaT
131602  215026851       0                  NaT
131603  215026851       1  1581120000000000000
131604  215026851       0                  NaT
131605  215026851       0                  NaT
131606  215026851       0                  NaT

我認為原因是錯誤。

標籤：Python 熊猫 日期 约会时间

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