I have a dataframe with columns of dates.
I know how to shift dates by a fixed number of months (eg add 3 months to all the dates in column x); however, I cannot figure out how to shift dates by a number of months which is not fixed, but is another column of the dataframe.
Any ideas?
I have copied a minimal example below. The error I get is:
The truth value of a Series is ambiguous
Thanks a lot!
import pandas as pd
import numpy as np
import datetime
df = pd.DataFrame()
df['year'] = np.arange(2000,2010)
df['month'] = 3
df['mydate'] = pd.to_datetime( (df.year * 10000 + df.month * 100 +1).apply(str), format='%Y%m%d')
df['month shift'] = np.arange(0,10)
# if I want to shift mydate by 3 months, I can convert it to DatetimeIndex and use dateOffset:
df['my date shifted by 3 months'] = pd.DatetimeIndex( df['mydate'] ) + pd.DateOffset(months = 3)
# however, how do I shift mydate by the number of months in the column 'month shift'?
#This does NOT work:
df['my date shifted'] = pd.DatetimeIndex( df['mydate'] ) + pd.DateOffset(months = df['month shift'])
print df
IIUC you could use apply with axis=1:
In [23]: df.apply(lambda x: x['mydate'] + pd.DateOffset(months = x['month shift']), axis=1)
Out[23]:
0 2000-03-01
1 2001-04-01
2 2002-05-01
3 2003-06-01
4 2004-07-01
5 2005-08-01
6 2006-09-01
7 2007-10-01
8 2008-11-01
9 2009-12-01
dtype: datetime64[ns]