Increase the date by number of months in pandas

Question

I have below pandas data frame

import pandas as pd
import numpy as np
dat = pd.DataFrame({'A' : [1,2,3,4,5], 'B' : ['2002-01-01', '2003-01-01', '2004-01-01', '2004-01-01', '2005-01-01']})
dat['A'] = dat['A'].astype('Int64')

Now I want to create another date column from column B by adding number of months from column A. Below is my code

pd.to_datetime(dat['B'], errors = 'coerce', dayfirst = True) + pd.DateOffset(months = dat['A'])

However with that, I get below error,

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "offsets.pyx", line 1382, in pandas._libs.tslibs.offsets.RelativeDeltaOffset.__init__
  File "offsets.pyx", line 328, in pandas._libs.tslibs.offsets._determine_offset
  File "/Users/abc/Python_VENV/lib/python3.12/site-packages/dateutil/relativedelta.py", line 172, in __init__
    if any(x is not None and x != int(x) for x in (years, months)):
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/abc/Python_VENV/lib/python3.12/site-packages/dateutil/relativedelta.py", line 172, in <genexpr>
    if any(x is not None and x != int(x) for x in (years, months)):
                                  ^^^^^^
  File "/Users/abc/Python_VENV/lib/python3.12/site-packages/pandas/core/series.py", line 248, in wrapper
    raise TypeError(f"cannot convert the series to {converter}")
TypeError: cannot convert the series to <class 'int'>

Could you please help to resolve this?

There is a "vectorized" approach here: stackoverflow.com/a/68367123 — jqurious
– jqurious, Commented Oct 14 at 9:42

Panda Kim · Accepted Answer · 2025-10-14 03:32:32Z

2

I think the simplest way to solve this problem is to use a loop.

Using apply

dat['B'] = pd.to_datetime(dat['B'], errors = 'coerce', dayfirst = True)
dat['C'] = dat.apply(lambda x: x['B'] + pd.DateOffset(months = x['A']), axis=1)

dat

        A   B           C
0   1   2002-01-01  2002-02-01
1   2   2003-01-01  2003-03-01
2   3   2004-01-01  2004-04-01
3   4   2004-01-01  2004-05-01
4   5   2005-01-01  2005-06-01

Using list comprehension

dat['B'] = pd.to_datetime(dat['B'], errors = 'coerce', dayfirst = True)
dat['C'] = [b + pd.DateOffset(months=a) for a, b in zip(dat['A'], dat['B'])]

same result.

answered Oct 14 at 3:32

Panda Kim

13.7k2 gold badges8 silver badges15 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Brian Smith Oct 14 at 4:45

Thanks. This works perfectly, but fairly slow for a large data frame

Panda Kim Oct 14 at 5:19

Yeah. That’s the limitation of loop.

Collectives™ on Stack Overflow

Increase the date by number of months in pandas

1 Answer 1

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related