Vectorized year/month/day operations with NumPy datetime64

Question

I would like to create vectors of NumPy datetime64 objects from 1-D vectors of years, months, and days, and also go the reverse direction, that is extracting vectors of year

Answer 1

This can be done with pandas without explicit looping (the code is taken from the pandas documentation):

 df = pd.DataFrame({'year': [2015, 2016],
   ....:                    'month': [2, 3],
   ....:                    'day': [4, 5],
   ....:                    'hour': [2, 3]})
   ....: 

In [32]: pd.to_datetime(df)
Out[32]: 
0   2015-02-04 02:00:00
1   2016-03-05 03:00:00
dtype: datetime64[ns]

of course you can 'floor' the date times to 'day' and return a numpy array with .values