Search and update values in other dataframe for specific columns

Question

I have two different dataframe in pandas.

First

A	B	C	D
1	2	3	5
1	5	3	2
2	5	3	2

Second

A	B	C	D	Value
5	3	3	2	1
1	5	4	3	1

I want column values A and B in the first dataframe to be searched in the second dataframe. If A and B values match then update the Value column.Search only 2 columns in other dataframe and update only 1 column. Actually the process we know in sql.

Result

A	B	C	D	VALUE
1	2	3	5	0
1	5	3	2	1
2	5	3	2	0

If you focus on the bold text, you can understand it more easily.Despite my attempts, I could not succeed. I only want 1 column to change but it also changes A and B. I only want the Value column of matches to change.

Does this answer your question? [pandas: merge (join) two data frames on multiple columns](https://stackoverflow.com/questions/41815079/pandas-merge-join-two-data-frames-on-multiple-columns) — Lucas M. Uriarte, Sep 06 '22 at 09:03
No because its change other A and B values too. Its creating duplicates — Thosifer MD, Sep 06 '22 at 09:20

score 0 · Answer 1 · answered Sep 06 '22 at 09:02

You can use a merge:

cols = ['A', 'B']
df1['VALUE'] = (df2.merge(df1[cols], on=cols, how='right')
                ['Value'].fillna(df1['VALUE'], downcast='infer')
               )

output:

   A  B  C  D  VALUE
0  1  2  3  5      0
1  1  5  3  2      1
2  2  5  3  2      0

Search and update values in other dataframe for specific columns

First

Second

Result

1 Answers1