我正在嘗試使用 loc 方法更新 pandas 數據框中選定的 datetime64 值來選擇滿足條件的行。但是，它不會分配新的日期時間值，而是生成 NaT。這是我的代碼的簡化，顯示了問題：import pandas as pdimport numpy as npdatetime = (np.datetime64('1899-12-30'), np.datetime64('1989-12-30'), np.datetime64('2199-12-30'))select = (0, 1, 0)df = pd.DataFrame(list(zip(datetime, select)),? ? ? ? ? ? ? ? ? columns=['date_time', 'select'])# create a new column by subtracting 180 daysdf['new_date'] = df['date_time'] - pd.Timedelta(180, unit='d')# replace datetime with new date where select is truedf.loc[(df['select'] == 1), ['date_time']] = df.loc[(df['select'] == 1), ['new_date']]print(df)# the second element of the date_time column is "NaT", but this is not the desired outcome.# the desired behaviour is for it to be the same as the second element in the new_date column.關于如何做到這一點或為什么這沒有按預期工作的任何想法？
1 回答
慕森卡
TA貢獻1806條經驗 獲得超8個贊
您應該[]在列名稱周圍放置：
df.loc[(df['select'] == 1), 'date_time'] = df.loc[(df['select'] == 1), 'new_date']
您還可以刪除第二個布爾索引：
df.loc[(df['select'] == 1), 'date_time'] = df['new_date']
另外，np.where：
df['date_time'] = np.where(df['select']==1, df['new_date'], df['date_time'])
說明：對數據幀df.loc[s, ['col_name']]進行切片，對系列進行切片。當你這樣做時：df.loc[s, 'col_name']
dataframe_slice = another_dataframe_slice
Pandas 將嘗試對齊兩個數據幀的索引/列。在這種情況下，兩個切片沒有公共列，因此更新后的數據幀的NaN值為select==1。
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