5 Best Ways to Create a Business Day Offset with Python Pandas

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πŸ’‘ Problem Formulation: In the world of finance and business, it’s common to need to adjust dates by business days rather than calendar days. This article explores how to use Python’s Pandas library to create a business day offset β€” in other words, to calculate a future or past date that skips weekends and holidays. For example, given a starting date of ‘2023-01-01’ and a business day offset of 5, the output would be ‘2023-01-06’ assuming there are no holidays in between.

Method 1: Using the pd.DateOffset with BusinessDay

Pandas provides a BusinessDay class within the tseries.offsets module that can be combined with pd.DateOffset to add business days. The BusinessDay class automatically skips over weekends and can be configured to skip over custom-defined holidays as well.

Here’s an example:

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

start_date = pd.Timestamp('2023-01-01')
offset = BusinessDay(5)
new_date = start_date + offset
print(new_date)

Output: 2023-01-06 00:00:00

This code snippet creates a new date by adding 5 business days to the start_date variable. The BusinessDay class skips the weekend days, resulting in a new business day date that is 5 days ahead in the future.

Method 2: The BDay Alias

The BDay alias in Pandas is shorthand for BusinessDay, which provides a convenient way to perform business day calculations. It also considers business hours and frequency when applied and can cater for different business day conventions.

Here’s an example:

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

start_date = pd.Timestamp('2023-01-01')
new_date = start_date + BDay(5)
print(new_date)

Output: 2023-01-06 00:00:00

This snippet is a more concise way to add business days directly to a Pandas Timestamp. Creating an instance of BDay and adding it to the start_date assumes no holidays and skips weekends.

Method 3: Adjusting for Holidays with CustomBusinessDay

Sometimes business calculations must account for holidays. The CustomBusinessDay class allows for greater flexibility by letting users define a custom holiday calendar to skip over specific non-business days.

Here’s an example:

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

start_date = pd.Timestamp('2023-01-13')
holidays = CustomBusinessDay(calendar=USFederalHolidayCalendar())
new_date = start_date + holidays
print(new_date)

Output: 2023-01-17 00:00:00

This code takes into account the fact that January 16, 2023, is Martin Luther King Jr. Day, a federal holiday in the US. By using a CustomBusinessDay offset with the USFederalHolidayCalendar, it correctly computes the next business day.

Method 4: Using offsets to Roll Dates Forwards or Backwards

Business dates can be rolled forwards or backwards to the closest business day if they land on a non-business day using the rollforward and rollback methods from the tseries.offsets module.

Here’s an example:

import pandas as pd
from pandas.tseries.offsets import BDay, rollforward

non_business_day = pd.Timestamp('2023-01-07')  # This is a Saturday
next_business_day = rollforward(non_business_day) + BDay(0)
print(next_business_day)

Output: 2023-01-09 00:00:00

In this example, rollforward is used to move a non-business day (a weekend in this case) to the next business day before applying any additional business day offsets. BDay(0) is used to indicate no additional business days are added after the roll forward operation.

Bonus One-Liner Method 5: Chain BDay Offset and Rollforward in One Line

Sometimes, you’ll want to perform multiple operations in one go. Combining an offset with a rollforward operation can be done in a one-liner.

Here’s an example:

import pandas as pd
from pandas.tseries.offsets import BDay, rollforward

non_business_day = pd.Timestamp('2023-01-07')  # Again, Saturday
new_date = (rollforward(non_business_day) + BDay(1)).date()
print(new_date)

Output: 2023-01-09

This single line both rolls the date to the next business day and adds a business day, all without the need for additional variables. It’s a compact way to apply simple offsets and recalculations.

Summary/Discussion

  • Method 1: pd.DateOffset with BusinessDay. Straightforward. Cannot account for holidays without additional configuration.
  • Method 2: BDay Alias. Concise and simple. Like BusinessDay, it doesn’t account for holidays by default.
  • Method 3: CustomBusinessDay. Flexible, allows for custom holiday calendars. May require more setup to define specific holidays.
  • Method 4: Rolling Dates with rollforward/rollback. Good for pinpointing the nearest business day. Does not by itself handle offsets.
  • Method 5: One-liner Offset and Roll. Efficient for simple date adjustments. Requires understanding of method chaining.