How to calculate Max value by Group in Python

Aggregation of fields is one of the basic necessity for data analysis and data science. Python’s Pandas module provide easy ways to do aggregation and calculate metrics. Finding maximum value for each group can also be achieved while doing the group by. The function that is helpful for finding the maximum value is max(). The below article explains with the help of an example How to calculate Max value by Group in Python.

John has store sales data available for analysis. There are five columns present in the data, Geography (country of store), Department (Industry category of the store), StoreID (Unique ID of each store), Time Period (Month of sales), Revenue (Total Sales for the month). John is looking forward to calculate maximum revenue for each stores. As there are 4 months of data available for each store, there will be one maximum value out of the four.

Find the maximum sales for each store in Pandas

• Step 1: Firstly, Import all the necessary modules.

import pandas as pd

• Step 2: Use max() function along with groupby operation. As we are looking forward to group by each StoreID, by=”StoreID” works as groupby parameter. The Revenue field contains the sales of each store. To find the maximum value, we will be using “Revenue” for maximum value calculation. For the current example, syntax is:

df1.groupby(by="StoreID")["Revenue"].max()

Example 2: Calculate Maximum value for each Department

• Here we are looking forward to calculate the maximum value across each department. So, the field in groupby operation will be “Department”

df1.groupby(by="Department")["Revenue"].max()

Thus, John is able to calculate values as per his requirement in Python.

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