Pandas: Split a given dataframe into groups and display target column as a list of unique values

Last update on April 04 2025 13:44:51 (UTC/GMT +8 hours)

20. Grouping with Unique Values as List

Write a Pandas program to split a given dataframe into groups and display target column as a list of unique values.

Test Data:

   id  type     book
0   A     1     Math
1   A     1     Math
2   A     1  English
3   A     1  Physics
4   A     2     Math
5   A     2  English
6   B     1  Physics
7   B     1  English
8   B     1  Physics
9   B     2  English
10  B     2  English

Sample Solution:

Python Code :

import pandas as pd
df = pd.DataFrame( {'id' : ['A','A','A','A','A','A','B','B','B','B','B'], 
                    'type' : [1,1,1,1,2,2,1,1,1,2,2], 
                    'book' : ['Math','Math','English','Physics','Math','English','Physics','English','Physics','English','English']})

print("Original DataFrame:")
print(df)
new_df = df[['id', 'type', 'book']].drop_duplicates()\
                         .groupby(['id','type'])['book']\
                         .apply(list)\
                         .reset_index()

new_df['book'] = new_df.apply(lambda x: (','.join([str(s) for s in x['book']])), axis = 1)
print("\nList all unique values in a group:")
print(new_df)

Sample Output:

Original DataFrame:
   id  type     book
0   A     1     Math
1   A     1     Math
2   A     1  English
3   A     1  Physics
4   A     2     Math
5   A     2  English
6   B     1  Physics
7   B     1  English
8   B     1  Physics
9   B     2  English
10  B     2  English

List all unique values in a group:
  id  type                  book
0  A     1  Math,English,Physics
1  A     2          Math,English
2  B     1       Physics,English
3  B     2               English

For more Practice: Solve these Related Problems:

• Write a Pandas program to group the dataframe by specific columns and then aggregate the target column into a comma-separated list of unique values.
• Write a Pandas program to split the dataframe into groups and then apply a function to convert group values into a list of distinct entries.
• Write a Pandas program to group by identifiers and then join the unique target values into a single string per group.
• Write a Pandas program to group the dataframe and then use a lambda function to aggregate the target column as a list of unique values.

Python Code Editor:

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