How to group dataframe rows into list in Pandas Groupby?

Suppose you have a Pandas DataFrame consisting of 2 columns and we want to group these columns. In this article, we will discuss the same. 

Creating Dataframe to group Dataframe rows into a list

Python3

# importing pandas as pd
import pandas as pd


# Create the data frame
df = pd.DataFrame({'column1': ['A', 'B', 'C', 'A', 'C',
                               'C', 'B', 'D', 'D', 'A'],
                   'column2': [5, 10, 15, 20, 25, 30,
                             35, 40, 45, 50]})
# Print the dataframe
df

Output:

Group rows into a list in Pandas using apply()

We can use groupby() method on column 1 and apply the method to apply a list on every group of pandas DataFrame.

Python3

# importing pandas as pd
import pandas as pd


# Create the data frame
df = pd.DataFrame({'column1': ['A', 'B', 'C', 'A', 'C',
                               'C', 'B', 'D', 'D', 'A'],
                   'column2': [5, 10, 15, 20, 25, 30,
                             35, 40, 45, 50]})


# Use groupby method and apply
# method on the dataframe
df = df.groupby('column1')['column2'].apply(list)

# Print the dataframe again
df

Output:

Group rows into a list in Pandas using lambda

We can use groupby() method on column 1 and agg() method to apply aggregation, consisting of the lambda function, on every group of pandas DataFrame.

Python3

# importing pandas as pd
import pandas as pd


# Create the dataframe
df = pd.DataFrame({'column1': ['A', 'B', 'C', 'A', 'C',
                               'C', 'B', 'D', 'D', 'A'],
                   'column2': [5, 10, 15, 20, 25, 30,
                               35, 40, 45, 50]})

# Use groupby method and agg method
# with lambda function on the dataframe
df = df.groupby('column1').agg({'column2': lambda x: list(x)})

# Print the dataframe again
df

Output:

Group rows into a list in Pandas using agg()

We can use the groupby() method on column1, and agg() method to apply the aggregation list, on every group of pandas DataFrame.

Python3

# importing pandas as pd
import pandas as pd


# Create the data frame
df = pd.DataFrame({'column1': ['A', 'B', 'C', 'A', 'C',
                               'C', 'B', 'D', 'D', 'A'],
                   'column2': [5, 10, 15, 20, 25, 30,
                               35, 40, 45, 50]})

# Use groupby method and agg method
# with list as argument on the dataframe
df = df.groupby('column1').agg(list)

df

Output:

Group rows into a list in Pandas using Pandas tolist

We can use groupby() method on column 1 and agg() method by passing ‘pd.Series.tolist’ as an argument.

Python3

# importing pandas as pd
import pandas as pd


# Create the data frame
df = pd.DataFrame({'column1': ['A', 'B', 'C', 'A', 'C',
                               'C', 'B', 'D', 'D', 'A'],
                   'column2': [5, 10, 15, 20, 25, 30,
                               35, 40, 45, 50]})

# Use groupby method and agg method with
# pd.Series.tolist as argument on the dataframe
df = df.groupby('column1').agg(pd.Series.tolist)

df

Output: