How to append a specific string according to each value in a string pandas dataframe column?

Question

Let's take these sample dataframes :

df = pd.DataFrame({'Id':['1','2','3','4','5'], 'Value':[9,8,7,6,5]})

  Id  Value
0  1      9
1  2      8
2  3      7
3  4      6
4  5      5

df_name = pd.DataFrame({'Id':['1','2','4'], 'Name':['Andrew','Jason','John']})

  Id    Name
0  1  Andrew
1  2   Jason
2  4    John

I would like to add in the Id column of df the Name of the person (obtainable in df_name) if it exists, in brackets. I know how to do this with a for loop over the Id column of df but it is inefficient with large dataframes. Do you know please a better way do to this ?

Expected output :

           Id  Value
0  1 (Andrew)      9
1   2 (Jason)      8
2           3      7
3    4 (John)      6
4           5      5

jezrael · Accepted Answer · 2021-01-14 09:52:26Z

1

Use Series.map for match values, add () and replace non matche values by original column in Series.fillna:

df['Id'] = ((df['Id'] + ' (' + df['Id'].map(df_name.set_index('Id')['Name']) + ')')
               .fillna(df['Id']))
print (df)
           Id  Value
0  1 (Andrew)      9
1   2 (Jason)      8
2           3      7
3    4 (John)      6
4           5      5

answered Jan 14, 2021 at 9:52

jezrael

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