Pandas: Subtracting two date columns and the result being an integer

Question

I have two columns in a Pandas data frame that are dates.

I am looking to subtract one column from another and the result being the difference in numbers of days as an integer.

A peek at the data:

df_test.head(10)
Out[20]: 
  First_Date Second Date
0 2016-02-09  2015-11-19
1 2016-01-06  2015-11-30
2        NaT  2015-12-04
3 2016-01-06  2015-12-08
4        NaT  2015-12-09
5 2016-01-07  2015-12-11
6        NaT  2015-12-12
7        NaT  2015-12-14
8 2016-01-06  2015-12-14
9        NaT  2015-12-15

I have created a new column successfully with the difference:

df_test['Difference'] = df_test['First_Date'].sub(df_test['Second Date'], axis=0)
df_test.head()         
Out[22]: 
  First_Date Second Date  Difference
0 2016-02-09  2015-11-19     82 days
1 2016-01-06  2015-11-30     37 days
2        NaT  2015-12-04         NaT
3 2016-01-06  2015-12-08     29 days
4        NaT  2015-12-09         NaT

However I am unable to get a numeric version of the result:

df_test['Difference'] = df_test[['Difference']].apply(pd.to_numeric)     

df_test.head()
Out[25]: 
  First_Date Second Date    Difference
0 2016-02-09  2015-11-19  7.084800e+15
1 2016-01-06  2015-11-30  3.196800e+15
2        NaT  2015-12-04           NaN
3 2016-01-06  2015-12-08  2.505600e+15
4        NaT  2015-12-09           NaN

Answer 1

How about:

df_test['Difference'] = (df_test['First_Date'] - df_test['Second Date']).dt.days

This will return difference as int if there are no missing values(NaT) and float if there is.

Pandas have a rich documentation on Time series / date functionality and Time deltas