Creating Custom Business Day Offsets with Python Pandas

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💡 Problem Formulation: When working with time series data in Python, you may need to define business days that deviate from the standard Monday to Friday schedule. For instance, you may want to consider a custom holiday calendar or skip certain weekdays. The pandas library offers flexibility in defining such schedules using CustomBusinessDay objects. An example input might be a dataset indexed by standard calendar dates, while the desired output would be the same dataset reindexed by a customized business day schedule.

Method 1: Using CustomBusinessDay with Custom Holidays

Creating a CustomBusinessDay object with custom holiday dates allows for precise business day calculations that respect specific non-working days. This is particularly useful for accounting for regional or company-specific holidays not covered by default holiday calendars.

Here’s an example:

import pandas as pd
from pandas.tseries.offsets import CustomBusinessDay
from pandas.tseries.holiday import AbstractHolidayCalendar, nearest_workday, Holiday

class MyHolidayCalendar(AbstractHolidayCalendar):
    rules = [
        Holiday('Custom New Year', month=1, day=1, observance=nearest_workday),
    ]

my_custom_calendar = MyHolidayCalendar()
my_bday = CustomBusinessDay(holidays=my_custom_calendar.holidays())
print(pd.date_range('2023-01-01', '2023-01-07', freq=my_bday))

Output:

DatetimeIndex(['2023-01-02', '2023-01-03', '2023-01-04', 
               '2023-01-05', '2023-01-06', '2023-01-09'], 
              dtype='datetime64[ns]', freq='C')

In this example, we define a custom holiday calendar with a New Year’s Day that is observed on the nearest working day. Using the CustomBusinessDay object with our custom holiday calendar, we generate a date range that skips the custom New Year’s holiday.

Method 2: Excluding Weekends and Special Weekdays

Sometimes, you may need to define business days while explicitly excluding weekends or certain weekdays. Python Pandas allows you to create a CustomBusinessDay object that can skip specific days of the week.

Here’s an example:

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

# Define a business day that skips weekends and Wednesdays
bday_without_wednesday = CustomBusinessDay(weekmask='Mon Tue Thu Fri')

# Generate 5 business days starting from 2023-01-01
print(pd.date_range('2023-01-01', periods=5, freq=bday_without_wednesday))

Output:

DatetimeIndex(['2023-01-02', '2023-01-03', '2023-01-05', 
               '2023-01-06', '2023-01-09'], 
              dtype='datetime64[ns]', freq='C')

By defining ‘weekmask’, we create a CustomBusinessDay object that considers Mondays, Tuesdays, Thursdays, and Fridays as business days, skipping both weekends and Wednesdays. The resulting date range demonstrates this custom definition.

Method 3: CustomBusinessDay with Weekmask and Holidays

You can combine custom weekly schedules with specific holiday dates for a highly tailored business day offset using Pandas CustomBusinessDay. This method provides the maximum control over defining business days for complex scheduling needs.

Here’s an example:

import pandas as pd
from pandas.tseries.offsets import CustomBusinessDay
from pandas.tseries.holiday import USFederalHolidayCalendar

# Define a CustomBusinessDay with both weekmask and Custom Holidays
weekmask = 'Mon Tue Wed Thu Fri'
holidays = ['2023-07-04', '2023-12-25']
my_custom_bday = CustomBusinessDay(holidays=holidays, weekmask=weekmask)

# Generate 10 business days starting from 2023-07-01
print(pd.date_range('2023-07-01', periods=10, freq=my_custom_bday))

Output:

DatetimeIndex(['2023-07-03', '2023-07-05', '2023-07-06', 
               '2023-07-07', '2023-07-10', '2023-07-11', 
               '2023-07-12', '2023-07-13', '2023-07-14', 
               '2023-07-17'], 
              dtype='datetime64[ns]', freq='C')

In the above snippet, we created a business day offset that respects a standard weekmask but also observes the 4th of July and Christmas as holidays. The date range generated does not include these holidays, demonstrating the combined effect.

Method 4: Adding Offsets to Dates

Pandas CustomBusinessDay can be used to add offsets to a series of dates, moving each date forward by a specified number of business days, while skipping weekends and holidays as needed.

Here’s an example:

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

bday = CustomBusinessDay()
series = pd.Series(pd.date_range('2023-01-01', periods=4, freq='D'))

# Add 3 custom business days to each date in the series
modified_series = series + 3 * bday
print(modified_series)

Output:

0   2023-01-04
1   2023-01-05
2   2023-01-08
3   2023-01-09
dtype: datetime64[ns]

Here, a standard CustomBusinessDay object is applied to a date range, adding three business days to each date and skipping weekends. The modified series reflects these adjusted dates.

Bonus One-Liner Method 5: Chaining CustomBusinessDay Constructs

For quick, on-the-fly adjustments, you can chain CustomBusinessDay constructors directly within operations to expedite date range modifications while maintaining readability.

Here’s an example:

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

# Generate a date range skipping weekends and adding a custom offset in one line
print(pd.date_range('2023-01-01', periods=5, freq=CustomBusinessDay(weekmask='Mon Tue Thu Fri')))

Output:

DatetimeIndex(['2023-01-02', '2023-01-03', '2023-01-05', 
               '2023-01-06', '2023-01-09'], 
              dtype='datetime64[ns]', freq='C')

This one-liner demonstrates the construction and usage of a CustomBusinessDay object with a defined weekmask inline with the date range function, offering a concise and efficient solution for generating business dates.

Summary/Discussion

  • Method 1: CustomBusinessDay with Custom Holidays. Ideal for non-standard holidays. May require additional setup to define custom holiday calendars.
  • Method 2: CustomBusinessDay Excluding Weekends and Special Weekdays. Useful for consistent weekly schedules. Does not account for one-off holidays.
  • Method 3: CustomBusinessDay with Weekmask and Holidays. Provides comprehensive control for combined weekly and holiday scheduling. More complex to implement.
  • Method 4: Adding Offsets to Dates. Effective for date arithmetic within existing date ranges. Requires pre-existing dates to apply offsets.
  • Method 5: Chaining CustomBusinessDay Constructs. Quick and readable for one-off calculations. Lacks customizability for more complex scenarios.