Python:Pandas .last()

The .last() method is an aggregation function used on a GroupBy object in Pandas. It returns the last non-null value in each section of the grouped data. This method is particularly useful for time-series data or sequentially ordered data where the final observation within a specific period or category is the most relevant.

Syntax

The method is called directly on a GroupBy object.

grouped_data.last(numeric_only=False, min_count=-1)

Parameters:

• numeric_only (bool): If True, only attempts to aggregate numeric columns.
• min_count (int): The required number of valid (non-NA) values to include the result. If fewer than min_count non-NA values are present, the result will be NaN.

Return value:

Returns a Series or DataFrame containing the last non-null value for each group.

Example

The following example demonstrates how to use .last() to find the final status of a task for each project:

import pandas as pd

# Create a DataFrame representing chronological task status updates
data = {
  'project_id': ['A', 'B', 'A', 'C', 'B', 'C', 'A'],
  'status_date': pd.to_datetime(['2025-01-01', '2025-01-05', '2025-01-10', '2025-01-15', '2025-01-20', '2025-01-25', '2025-01-30']),
  'task_status': ['Start', 'Pending', 'In Progress', 'Start', 'Completed', 'In Progress', 'Completed']
}
df = pd.DataFrame(data).set_index('status_date').sort_index()

print("Original Data:\n", df)

# Group by project_id and find the last status (chronologically) for each project
last_status = df.groupby('project_id').last()

print("\nLast Status by Project:\n", last_status)

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The above code returns the following output:

Original Data:
                   project_id  task_status
status_date
2025-01-01                   A        Start
2025-01-05                   B      Pending
2025-01-10                   A  In Progress
2025-01-15                   C        Start
2025-01-20                   B    Completed
2025-01-25                   C  In Progress
2025-01-30                   A    Completed

Last Status by Project:
              task_status
project_id
A              Completed
B              Completed
C          In Progress

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Codebyte Example

This codebyte example groups data by category and returns the last recorded value from each group:

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