Calculate Last Friday of Month in Pandas

Question

I\'ve written this function to get the last Thursday of the month

def last_thurs_date(date):
    month=date.dt.month
    year=date.dt.year
    
    cal = cale         


        

Answer 1

• This question answer Calculate Last Friday of Month in Pandas
  • This can be modified by selecting the appropriate day of the week, here freq='W-FRI'
• I think the easiest way is to create a pandas.DataFrame using pandas.date_range and specifying freq='W-FRI.
  • W-FRI is Weekly Fridays
  • pd.date_range(df.Date.min(), df.Date.max(), freq='W-FRI')
    • Creates all the Fridays in the date range between the min and max of the dates in df
  • Use a .groupby on year and month, and select .last(), to get the last Friday of every month for every year in the date range.
• Because this method finds all the Fridays for every month in the range and then chooses .last() for each month, there's not an issue with trying to figure out which week of the month has the last Friday.
• With this, use pandas: Boolean Indexing to find values in the Date column of the dataframe that are in last_fridays_in_daterange.
  • Use the .isin method to determine containment.
• pandas: DateOffset objects

import pandas as pd

# test data: given a dataframe with a datetime column
df = pd.DataFrame({'Date': pd.date_range(start=pd.to_datetime('2014-01-01'), end=pd.to_datetime('2020-08-31'), freq='D')})

# create a dateframe with all Fridays in the daterange for min and max of df.Date
fridays = pd.DataFrame({'datetime': pd.date_range(df.Date.min(), df.Date.max(), freq='W-FRI')})

# use groubpy and last, to get the last Friday of each month into a list
last_fridays_in_daterange = fridays.groupby([fridays.datetime.dt.year, fridays.datetime.dt.month]).last()['datetime'].tolist()

# find the data for the last Friday of the month
df[df.Date.isin(last_fridays_in_daterange)]