Pandas 填充最近日期的值

Question

I have two dataframes, and I want to add the values from the first dataframe to the second one based on the most recent date that was found. Is there a built in method in pandas to do it?

Sample code:

df1 = pd.DataFrame( {'Time': pd.to_datetime(['1-1-2018', '1-1-2019']), 'Value':[1,2]})
df2 = pd.DataFrame( {'Time': pd.to_datetime(['1-23-2018', '1-22-2019'])} )
df3 = pd.DataFrame( {'Time': pd.to_datetime(['1-23-2018', '1-22-2019']), 'Value':[1,2]} )

display(df1)
display(df2)
print()
print('how to get df3 from df1 and df2?')
display(df3)

Answer 1

merge_asof provides capability you want

df1 = pd.DataFrame( {'Time': pd.to_datetime(['1-1-2018', '1-1-2019']), 'Value':[1,2]})
df2 = pd.DataFrame( {'Time': pd.to_datetime(['1-23-2018', '1-22-2019'])} )
pd.merge_asof(df2, df1, on="Time")

	Time	Value
0	2018-01-23 00:00:00	1
1	2019-01-22 00:00:00	2