Pandas 中的 Excel VLOOKUP 等效项
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Excel VLOOKUP equivalent in pandas
提问by Al_Iskander
I have following dataframe:
我有以下数据框：
A B C
Index
2001-06-30 100 2001-08-31 (=value of A at date B)
2001-07-31 200 2001-09-30 ...
2001-08-31 300 2001-10-31 ...
2001-09-30 400 2001-11-30 ...
Column Bconsists of dates from column Ashifted forward by some. I would like to generate column Cthat consists of the values from column Aon date B. (preferably in the logic the Excel VLOOKUP formula would do it. I am not looking for simply shift(-2)here because in reality the shift between Band Indexis not always equal).
列B由A前移一些列的日期组成。我想生成C由Adate列中的值组成的列B。（最好是在逻辑中的Excel VLOOKUP公式会做到这一点。我不是在寻找简单的shift(-2)这里，是因为在现实之间的转移B和Index并不总是等于）。
I tried df.loc['B', 'A']but this most probably too simplistic and produced an error.
我试过了，df.loc['B', 'A']但这很可能太简单了并产生了错误。
回答by jezrael
I think you need mapby column A:
我认为您需要map按列A：
df['C'] = df.B.map(df.A)
print (df)
A B C
Index
2001-06-30 100 2001-08-31 300.0
2001-07-31 200 2001-09-30 400.0
2001-08-31 300 2001-10-31 NaN
2001-09-30 400 2001-11-30 NaN
It is same as:
它与：
df['C'] = df.B.map(df.A.to_dict())
print (df)
A B C
Index
2001-06-30 100 2001-08-31 300.0
2001-07-31 200 2001-09-30 400.0
2001-08-31 300 2001-10-31 NaN
2001-09-30 400 2001-11-30 NaN
