How to List values for each Pandas group?

Last Updated : 20 Aug, 2020

In this article, we'll see how we can display all the values of each group in which a dataframe is divided. The dataframe is first divided into groups using the DataFrame.groupby() method. Then we modify it such that each group contains the values in a list.

First, Let's create a Dataframe:

Python3

# import pandas library
import pandas as pd

# create a dataframe
df = pd.DataFrame({'a': ['A', 'A', 'B',
                          'B', 'B', 'C',
                          'C', 'D'], 
                    'b': [1, 2, 5,
                          3, 5, 4,
                          8, 6]})
# show the dataframe                  
df

Output:

Method 1: Using DataFrame.groupby() and Series.apply() together.
Example: We'll create lists of all values of each group and store it in new column called “listvalues”.

Python3

# import pandas library
import pandas as pd

# create a dataframe
df = pd.DataFrame({'a': ['A', 'A', 'B',
                          'B', 'B', 'C',
                          'C', 'D'], 
                    'b': [1, 2, 5,
                          3, 5, 4,
                          8, 6]})
                 
# convert values of each group
# into a list
groups = df.groupby('a')['b'].apply(list)

print(groups)

# groups store in a new 
# column called listvalues
df1 = groups.reset_index(name 
                         = 'listvalues')
# show the dataframe
df1

Output:

Method 2: Using DataFrame.groupby() and Series.agg().

Example: We use the lambda function inside the Series.agg() to convert the all values of a group to a list.

Python3

# import pandas library
import pandas as pd

# create a dataframe
df = pd.DataFrame( {'a': ['A', 'A', 'B',
                         'B', 'B', 'C', 
                         'C', 'D'], 
                    'b': [1, 2, 5, 
                         3, 5, 4,
                         8, 6]}
                 )
# convert values of each group
# into a list
groups = df.groupby('a').agg(lambda
                             x: list(x))

print(groups)