从一个数据帧中提取数据并将其添加到第二个数据帧

Question

I am a python beginner. I have two data frames, df1 , df2 . there are some duplicates ( apple , grape ), so I want to add the users info from df2 and add it to df1 , but only to the duplicates. at the end i should have a new df1 with apple and grape rows with new data( i know i would have to create a new column 'USERS' in df1) Any help is appreciated

import pandas as pd

df1 = pd.DataFrame({'FRUIT':['banana','apple', 'grape'], 'COLOR':['yellow', 'red', 'green'], 'CAL':[100, 80, 100]})
df2 = pd.DataFrame({'FRUIT':['kiwi','melon', 'apple', 'grape', 'pineapple'], 'COLOR':['green', 'orange', 'red',\
                    'blue','yellow'], 'CAL':[60, 70, 80, 50, 80], 'USERS':[4, 7, 12, 20, 3]})


df = pd.concat([df1,df2], keys=['df1','df2'], sort=False)

col_val_to_add = df[df.duplicated(['FRUIT'])]

for i in df:
    for j in col_val_to_add:
        if df.loc[['FRUIT',i]]==df.loc[['FRUIT',j]]:
            df.loc[['USERS',j]] = col_val_to_add.loc[['USERS',i]]
print(df)

Answer 1

What you are hoping to do is called a join (specifically a LEFT join). In pandas you can do this with merge:

new_df = df1.merge(df2[['FRUIT', 'USERS']], on="FRUIT", how="left")

Hope that helps.

EDIT: Sorry I just re-read your questions. If you want only the FRUIT that are in both dfs switch the left join to an inner join like this:

new_df = df1.merge(df2[['FRUIT', 'USERS']], on="FRUIT", how="inner")