Python - How to Group Pandas DataFrame by Month?

We will group Pandas DataFrame using the groupby. Select the column to be used using the grouper function. We will group month-wise and calculate sum of Registration Price monthly for our example shown below for Car Sale Records.

At first, let’s say the following is our Pandas DataFrame with three columns −

dataFrame = pd.DataFrame(
   {
      "Car": ["Audi", "Lexus", "Tesla", "Mercedes", "BMW", "Toyota", "Nissan", "Bentley", "Mustang"],

      "Date_of_Purchase": [
         pd.Timestamp("2021-06-10"),
         pd.Timestamp("2021-07-11"),
         pd.Timestamp("2021-06-25"),      
         pd.Timestamp("2021-06-29"),
         pd.Timestamp("2021-03-20"),
         pd.Timestamp("2021-01-22"),  
         pd.Timestamp("2021-01-06"),
         pd.Timestamp("2021-01-04"),
         pd.Timestamp("2021-05-09")
      ],
     "Reg_Price": [1000, 1400, 1100, 900, 1700, 1800, 1300, 1150, 1350]
   }
)

Use the Grouper to select Date_of_Purchase column within groupby() function. The frequency freq is set ‘M’ to group by month-wise −

print("\nGroup Dataframe by month...\n",dataFrame.groupby(pd.Grouper(key='Date_of_Purchase', axis=0, freq='M')).sum())

Example

Following is the code −

import pandas as pd

# dataframe with one of the columns as Date_of_Purchase
dataFrame = pd.DataFrame(
    {
      "Car": ["Audi", "Lexus", "Tesla", "Mercedes", "BMW", "Toyota", "Nissan", "Bentley", "Mustang"],

      "Date_of_Purchase": [
         pd.Timestamp("2021-06-10"),
         pd.Timestamp("2021-07-11"),
         pd.Timestamp("2021-06-25"),
         pd.Timestamp("2021-06-29"),
         pd.Timestamp("2021-03-20"),
         pd.Timestamp("2021-01-22"),
         pd.Timestamp("2021-01-06"),
         pd.Timestamp("2021-01-04"),
         pd.Timestamp("2021-05-09")
      ],

      "Reg_Price": [1000, 1400, 1100, 900, 1700, 1800, 1300, 1150, 1350]
   }
)

print"DataFrame...\n",dataFrame

# Grouper to select Date_of_Purchase column within groupby function
print"\nGroup Dataframe by month...\n",dataFrame.groupby(pd.Grouper(key='Date_of_Purchase', axis=0, freq='M')).sum()

Output

This will produce the following output. The Registration price of every month gets calculated −

DataFrame...
     Car     Date_of_Purchase     Reg_Price
0     Audi     2021-06-10            1000
1    Lexus     2021-07-11            1400
2    Tesla     2021-06-25            1100
3 Mercedes     2021-06-29             900
4      BMW     2021-03-20            1700
5   Toyota     2021-01-22            1800
6   Nissan     2021-01-06            1300
7  Bentley     2021-01-04            1150
8  Mustang     2021-05-09            1350
 Group Dataframe by month...
                    Reg_Price
Date_of_Purchase
2021-01-31             4250.0
2021-02-28                NaN
2021-03-31             1700.0
2021-04-30                NaN
2021-05-31             1350.0
2021-06-30             3000.0
2021-07-31             1400.0