How to change values in the common elements between 2 dataframes?

Question

I have a df called df1 like this:

        NAME       CODE       TYPE ........... many other columns
        object1   20052020     A
        object2   20082021     B
        object3   20012031     B
        object4   20010123     C
           .         .         .
           .         .         .
           .         .         .
          etc       etc       etc

and i have another df called df2:

         NAME      CODE    ........... many other columns
        object1  20052020
        object2  20082021 
           .         .

I want to change the TYPE values in df1. I want to make this change only in the common elements between df2 and df1 BY CODE, like this (i changed A type for F type in the common elements):

        NAME       CODE       TYPE ........... many other columns
        object1   20052020     F
        object2   20082021     F
        object3   20012031     B
        object4   20010123     C
           .         .         .
           .         .         .
           .         .         .
          etc       etc       etc

Answer 1

Use DataFrame.merge with boolean indexing :

df1 = df1.merge(df2['CODE'], on='CODE', how='left', indicator=True)
df1.loc[df1.pop('_merge').eq('both'), 'TYPE'] = 'F'

OR use Series.map with Series.fillna ,

df1['TYPE']=(
    df1['CODE'].map(
        df2.set_index('CODE').assign(TYPE='F').pop('TYPE'))
    .fillna(df1['TYPE'])
)

Result:

# print(df1)

    NAME    CODE     TYPE
0   object1 20052020    F
1   object2 20082021    F
2   object3 20012031    B
3   object4 20010123    C

Answer 2

Try:

df.set_index('CODE', inplace=True)
df1.set_index('CODE', inplace=True)

df.loc[df.index & df1.index, 'TYPE'] = 'F'
df.reset_index()

---

CODE        NAME    TYPE                
20052020    object1 F
20082021    object2 F
20012031    object3 B
20010123    object4 C

---

Don't forget to reset the index