How to merge two dataframes with inner join, without having duplicate columns?

user_16963595 0
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I have a dataframe like :

ItemName Category
item1    cat1
item2    cat1
item3    cat1
item4    cat1
item5    cat2
item6    cat2

and one like:

CategoryName Element
cat1         element1
cat2         element2

I want to merge both dataframes into one, based on the category column, but now I have two columns having the categories. This would be the ideal result:

ItemName Category Element
item1    cat1     element1
item2    cat1     element1
item3    cat1     element1
item4    cat1     element1
item5    cat2     element2
item6    cat2     element2

But I have the result with duplicate of column Category and CategoryName. How to solve this duplicate issue when merging the dataframes? What I did for the merge:

result_df= df1.merge(
    df2,
    left_on='Category',
    right_on='CategoryName',
    how='inner')
pandas inner-join merge python
2 Answers

Unfortunately you would need to rename the columns:

>>> df1.merge(df2.rename({'CategoryName': 'Category'}, axis=1), on='Category')
  ItemName Category   Element
0    item1     cat1  element1
1    item2     cat1  element1
2    item3     cat1  element1
3    item4     cat1  element1
4    item5     cat2  element2
5    item6     cat2  element2
>>>

Or you have to drop it:

>>> df1.merge(df2, left_on='Category', right_on='CategoryName').drop('CategoryName', axis=1)
  ItemName Category   Element
0    item1     cat1  element1
1    item2     cat1  element1
2    item3     cat1  element1
3    item4     cat1  element1
4    item5     cat2  element2
5    item6     cat2  element2
>>>
user_87083640

You can use pd.Series.map:

df["Element"] = df["Category"].map(df2.set_index("CategoryName")["Element"])

print (df)

  ItemName Category   Element
0    item1     cat1  element1
1    item2     cat1  element1
2    item3     cat1  element1
3    item4     cat1  element1
4    item5     cat2  element2
5    item6     cat2  element2
user_92844230
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