如何用 pandas 中日期列中的最大日期填充缺失的日期？

Question

I am trying to fill a missing value in a date column with the max of the date in the same column. however with the below code provided, it is not getting transformed.

us_copy['Inv_Latest_Document_Date'] = us_copy['Inv_Latest_Document_Date'].fillna(us_copy.groupby('Vendor_Name')['Inv_Latest_Document_Date'].max())

Answer 1

Use GroupBy.transform for Series with same size like original:

#if necessary convert to datetimes
us_copy['Inv_Latest_Document_Date'] = pd.to_datetime(us_copy['Inv_Latest_Document_Date'])

s = us_copy.groupby('Vendor_Name')['Inv_Latest_Document_Date'].transform('max')
us_copy['Inv_Latest_Document_Date'] = us_copy['Inv_Latest_Document_Date'].fillna(s)

EDIT: If need repalce by max of all column values:

#if necessary convert to datetimes
us_copy['Inv_Latest_Document_Date'] = pd.to_datetime(us_copy['Inv_Latest_Document_Date'])

a = us_copy['Inv_Latest_Document_Date'].max()
us_copy['Inv_Latest_Document_Date'] = us_copy['Inv_Latest_Document_Date'].fillna(a)