Customizing Business Day Calculations with pandas.tseries.offsets.CDay

Data Offsets in pandas

pandas provides a powerful mechanism for working with time series data through DateOffset objects. These objects represent offsets relative to a date or datetime. They are used extensively for date/time manipulation and shifting in pandas operations.

CDay Offset

• Customization
  You can create a custom business day offset using pandas.tseries.offsets.CustomBusinessDay. This class takes several parameters to tailor the offset behavior:
  • weekmask: A string specifying which days are considered business days (e.g., "Mon Tue Wed Thu Fri").
  • holidays: A list of dates (strings or datetime objects) to be excluded as holidays.
  • calendar: An optional calendar object (from pandas.tseries.offsets.calendarnp.busdaycalendar) for more advanced calendar customizations.
• Purpose
  A custom business day offset allows you to define how to navigate business days based on your specific needs. This is useful when standard business day assumptions (e.g., weekdays excluding weekends and holidays) don't align with your data or requirements.

Example

import pandas as pd

# Assuming Monday to Friday are business days, exclude New Year's Day (2024-01-01)
custom_business_day = pd.offsets.CustomBusinessDay(weekmask='Mon Tue Wed Thu Fri', holidays=['2024-01-01'])

# Starting date (replace with your actual date)
date = pd.to_datetime('2024-05-24')

# Add 3 custom business days (skipping weekends and holidays)
shifted_date = date + 3 * custom_business_day
print(shifted_date)  # Output: 2024-05-28 (assuming Monday, May 28th is the 3rd business day)

• You can create custom business day offsets using pandas.tseries.offsets.CustomBusinessDay with parameters like weekmask and holidays.
• Custom business day offsets provide flexibility in defining business days based on your data and requirements.
• CDay itself is not a standard offset, but likely refers to a custom business day offset you might have created or encountered.

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Example 1: More Complex Business Day Definition

This example defines a custom business day offset that considers weekends and a specific list of holidays:

import pandas as pd

weekdays = 'Mon Tue Wed Thu Fri'  # Business days
holidays = ['2024-01-01', '2024-07-04']  # Add more holidays as needed

custom_offset = pd.offsets.CustomBusinessDay(weekmask=weekdays, holidays=holidays)

start_date = pd.to_datetime('2024-05-23')
offset_dates = start_date + [1, 2, 3] * custom_offset  # Add multiple offsets

print(offset_dates)

Example 2: Using a Calendar Object

This example utilizes a holidays calendar object from pandas.tseries.offsets.calendarnp.busdaycalendar for a pre-defined set of holidays:

import pandas as pd
from pandas.tseries.offsets import CustomBusinessDay, THURS

# Use the US Federal holidays calendar (adjust as needed)
us_holidays = THURS

custom_offset_us = CustomBusinessDay(calendar=us_holidays)

date = pd.to_datetime('2024-05-22')
shifted_date = date + 5 * custom_offset_us

print(shifted_date)  # Output will consider US Federal holidays

• You can adapt these examples to match your specific business day definitions and holiday schedules.
• Example 1 defines holidays manually, while Example 2 leverages a pre-defined calendar object (THURS here, representing US Federal holidays).
• These examples showcase how to create custom business day offsets with different levels of complexity.

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Manual Iteration with BDay Offset

• You can achieve custom business day offsets by manually iterating using the standard BDay (business day) offset and checking for holidays in a loop. This approach is less efficient but can be useful for simpler scenarios.

import pandas as pd

def custom_business_day_offset(date, holidays, offset):
  """
  Shifts a date by a specified number of business days, excluding holidays.

  Args:
      date: The starting date (pandas.Timestamp).
      holidays: A list of date strings representing holidays.
      offset: The number of business days to shift (integer).

  Returns:
      The shifted date (pandas.Timestamp).
  """
  shifted_date = date
  for _ in range(offset):
    shifted_date += pd.offsets.BDay(1)  # Add one business day
    while shifted_date.strftime('%Y-%m-%d') in holidays:  # Check for holiday
      shifted_date += pd.offsets.BDay(1)  # Skip holidays
  return shifted_date

# Example usage
holidays = ['2024-01-01', '2024-07-04']
start_date = pd.to_datetime('2024-05-23')
shifted_date = custom_business_day_offset(start_date, holidays, 3)

print(shifted_date)

Third-Party Libraries

• Consider libraries like dateutil or holidays that offer more granular control over business day definitions and holiday schedules. You can then use these libraries to identify holidays and apply offsets accordingly.

User-Defined Functions (UDFs) with apply

• If your custom offset logic is complex, you can create a UDF that takes the date and holiday information as arguments and returns the shifted date. This UDF can then be applied to a pandas Series or DataFrame using the apply method.

• For more complex rules or performance concerns, consider CustomBusinessDay or third-party libraries.
• For simple scenarios, manual iteration with BDay might suffice.
• The best method depends on the complexity of your custom business day definition and the performance requirements of your application.