[英]Python - Get most recent date in a pandas dataframe
我必須在數據框熊貓中獲取最新日期。 我寫了這段代碼:
df=pd.read_csv('waterquality.csv')
# Convert date to datetime type
df['SampleDate'] = df['SampleDate'].astype('datetime64[ns]')
#print(df.SampleDate.max())
g=df.groupby(['name','beach','ParameterCode']).SampleDate.max()
print(g)
輸出是:
[...]
Seal Beach Seal Beach Pier Enterococcus 2018-12-09
Total Coliforms 2018-12-09
但日期不是最近的。 誰能幫我? 謝謝
我測試了你的代碼,它似乎工作,你能提供一個例子,它不是:
df = pd.DataFrame({'name': ['Seal Beach']*4, 'beach':['Seal Beach Pier']*4, 'ParameterCode':['Enterococcus']*2 + ['Total Coliforms']*2, 'SampleDate':['2018-12-09','2018-12-10','2018-12-09','2018-12-10']})
df
name beach ParameterCode SampleDate
0 Seal Beach Seal Beach Pier Enterococcus 2018-12-09
1 Seal Beach Seal Beach Pier Enterococcus 2018-12-10
2 Seal Beach Seal Beach Pier Total Coliforms 2018-12-09
3 Seal Beach Seal Beach Pier Total Coliforms 2018-12-10
df['SampleDate'] = df['SampleDate'].astype('datetime64[ns]')
df.groupby(['name', 'beach', 'ParameterCode']).SampleDate.max()
name beach ParameterCode
Seal Beach Seal Beach Pier Enterococcus 2018-12-10
Total Coliforms 2018-12-10
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