Count the Number of Rows in Each Group using Python Pandas

Use the group.size() to count the number of rows in each group. Import the required library −

import pandas as pd

Create a DataFrame −

dataFrame = pd.DataFrame({'Product Category': ['Computer', 'Mobile Phone', 'Electronics', 'Electronics', 'Computer', 'Mobile Phone'],'Quantity': [10, 50, 10, 20, 25, 50],'Product Name': ['Keyboard', 'Charger', 'SmartTV', 'Camera', 'Graphic Card', 'Earphone']
})

Group by columns −

dataFrame.groupby(["Product Category", "Quantity"])

Now, count the group size to get the count of rows in each group.

Example

Following is the complete code −

import pandas as pd

# create a dataframe
dataFrame = pd.DataFrame({'Product Category': ['Computer', 'Mobile Phone', 'Electronics', 'Electronics', 'Computer', 'Mobile Phone'],'Quantity': [10, 50, 10, 20, 25, 50],'Product Name': ['Keyboard', 'Charger', 'SmartTV', 'Camera', 'Graphic Card', 'Earphone']
})

# dataframe
print"Dataframe...\n",dataFrame

# grouping columns
new_group = dataFrame.groupby(["Product Category", "Quantity"])

# group size
new_group = new_group.size()

# dataframe
print"\nUpdated Dataframe...\n",new_group

Output

This will produce the following output −

Dataframe...
   Product Category   Product Name   Quantity
0          Computer       Keyboard         10
1      Mobile Phone        Charger         50
2       Electronics        SmartTV         10
3       Electronics         Camera         20
4          Computer   Graphic Card         25
5      Mobile Phone       Earphone         50

Updated Dataframe...
Product Category   Quantity
Computer           10        1
                   25        1
Electronics        10        1
                   20        1
Mobile Phone       50        2
dtype: int64