Calculating the amount of full months between two dates?

user_9536834 0
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First and last dates of a time series are as follows:

firstday = transactions["Date"].head(1)
firstday
lastday = transactions["Date"].tail(1)
lastday

Dateindex
2017-12-30   2017-12-30
Name: Date, dtype: datetime64[ns]
Dateindex
2018-12-31   2018-12-31
Name: Date, dtype: datetime64[ns]

I want the following two things:

1) get firstday and lastday as "2017-12-30" and "2018-12-31" (strings), instead of dtype('<M8[ns]')

2) calculate the number of whole months between these dates (correct output would be 12 months)

Any ideas how to achieve these? Thank you.

python-datetime pandas datetime python
2 Answers

Select first and last value by Series.iat:

firstday = transactions["Date"].iat[0]
lastday = transactions["Date"].iat[-1]

Alternative is use Index.get_loc for position for column Date with DataFrame.iat:

firstday = transactions.iat[0, transactions.columns.get_loc('Date')]
lastday = transactions.iat[-1, transactions.columns.get_loc('Date')]

print (firstday)
2017-12-30 00:00:00

print (lastday)
2018-12-31 00:00:00

For difference convert timestamp to month period by Timestamp.to_period and subtract:

diff = lastday.to_period('m') - firstday.to_period('m')
print (diff)
12
user_29010020

Here is for you information

firstdayStr = str(firstday[0])
lastdayStr = str(lastday[0])

months = (lastday[0].year - firstday[0].year) * 12 + lastday[0].month - firstday[0].month

output 

2017-12-30 00:00:00  
2018-12-31 00:00:00  
12
user_46436090
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