company_id,company_name
1,Amazon
1,Amazon Ltd
2,Google
1,Amazon
2,Gogle
3,Facebook Ltd
3,Facebook LTD
1,AMAZON
1,AMAZON LTD
2,GOOGLE
3,Facebook
3,Face book

company_id,company_name
1,Amazon
1,Amazon
2,Google
1,Amazon
2,Google
3,Facebook
3,Facebook
1,Amazon
1,Amazon
2,Google
3,Facebook
3,Facebook

dd = df.drop_duplicates().set_index('company_id').to_dict()['company_name']
df.company_name = df.company_id
df.company_name = df.company_name.replace(dd)