How to find the difference between two dates in years

Question

I have two columns in my dataframe that I have converted into datetime. I’m trying to subtract these numbers and find the difference in years. This is the code I’m using:

from dateutil.relativedelta import relativedelta
difference_in_years = relativedelta(x['start'], x['end']).year

However, I’m getting the following error message:

ValueError: The truth value of a Series is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().

What is the issue?

Asked By: HHH

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Source

Answer 1

Use attribute .years with apply and axis=1 for process by rows:

df = pd.DataFrame({'start':['2015-10-02','2014-11-05'],
                   'end':['2018-01-02','2018-10-05']})

df['start'] = pd.to_datetime(df['start'])
df['end'] = pd.to_datetime(df['end'])

from dateutil.relativedelta import relativedelta

df['y'] = df.apply(lambda x: relativedelta(x['end'], x['start']).years, axis=1)

Or use list comprehension:

df['y'] = [relativedelta(i, j).years for i, j in zip(df['end'], df['start'])]

print (df)
       start        end  y
0 2015-10-02 2018-01-02  2
1 2014-11-05 2018-10-05  3

EDIT:

df = pd.DataFrame({'start':['2015-10-02','2014-11-05'],
                   'end':['2018-01-02',np.nan]})

df['start'] = pd.to_datetime(df['start'])
df['end'] = pd.to_datetime(df['end'])

from dateutil.relativedelta import relativedelta

m = df[['start','end']].notnull().all(axis=1)
df.loc[m, 'y'] = df[m].apply(lambda x: relativedelta(x['end'], x['start']).years, axis=1)
print (df)
       start        end    y
0 2015-10-02 2018-01-02  2.0
1 2014-11-05        NaT  NaN

Answered By: jezrael

Answer 2

Check this answer calculate the difference between two datetime.date() dates in years and months

from dateutil import relativedelta as rdelta
from datetime import date
d1 = date(2001,5,1)
d2 = date(2012,1,1)
rd = rdelta.relativedelta(d2,d1)
rd
relativedelta(years=+10, months=+8)

Answered By: Jorge

Answer 3

You can do it by

(df['end'] - df['start'])/pd.Timedelta(1, 'Y')

and round the result if needed.

In pandas v0.23.4 and later you can do

(df['end'] - df['start'])//pd.Timedelta(1, 'Y')

to get whole year difference straight away.

Update: In panda v0.25 and later, pd.Timedelta(1, 'Y') is not supported, because a year is not a consistent unit of measure (sometimes 365d, sometimes 366d). You can do this instead if the 365d approximation is acceptable:

(df['end'] - df['start'])/pd.Timedelta(365, 'D')

Answered By: ayorgo

Answer 4

You can divide a timedelta series by year units and, if necessary, round:

# data from jezrael

df['years'] = (df['end'] - df['start']) / np.timedelta64(1, 'Y')
df['years_floor'] = df['years'].round()

print(df)

       start        end     years  years_floor
0 2015-10-02 2018-01-02  2.253297          2.0
1 2014-11-05        NaT       NaN          NaN

Answered By: jpp

How to find the difference between two dates in years

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