Days between dates

Q: how many days are there in between these days ?

'29 sep 2016', '7 jul 2016', '28 apr 2016', '10 mar 2016', '14 jan 2016'

Solution:

from datetime import datetime,timedelta

a=map(lambda x: datetime.strptime(x,'%d %b %Y'),
      ['29 sep 2016', '7 jul 2016', '28 apr 2016', '10 mar 2016', '14 jan 2016'] ) 

def dr(ar):
    if len(ar)>1:
        print "{:%d %b %Y} .. {} .. {:%d %b %Y} ".format(
                            ar[0], (ar[0]-ar[1]).days, ar[1])
        dr(ar[1:]) 

Output:

dr(a) 

29 Sep 2016 .. 84 .. 07 Jul 2016 
07 Jul 2016 .. 70 .. 28 Apr 2016 
28 Apr 2016 .. 49 .. 10 Mar 2016 
10 Mar 2016 .. 56 .. 14 Jan 2016 

Dataframe with date-time index

Create a dataframe df with a datetime index and some random values: (note: see 'simpler' dataframe creation further down)

Output:

    In [4]: df.head(10)
    Out[4]: 
                value
    2009-12-01     71
    2009-12-02     92
    2009-12-03     64
    2009-12-04     55
    2009-12-05     99
    2009-12-06     51
    2009-12-07     68
    2009-12-08     64
    2009-12-09     90
    2009-12-10     57
    [10 rows x 1 columns]

Now select a week of data

Output: watchout selects 8 days!!

    In [235]: df[d1:d2]
    Out[235]: 
                value
    2009-12-10     99
    2009-12-11     70
    2009-12-12     83
    2009-12-13     90
    2009-12-14     60
    2009-12-15     64
    2009-12-16     59
    2009-12-17     97
    [8 rows x 1 columns]


    In [236]: df[d1:d1+dt.timedelta(days=7)]
    Out[236]: 
                value
    2009-12-10     99
    2009-12-11     70
    2009-12-12     83
    2009-12-13     90
    2009-12-14     60
    2009-12-15     64
    2009-12-16     59
    2009-12-17     97
    [8 rows x 1 columns]


    In [237]: df[d1:d1+dt.timedelta(weeks=1)]
    Out[237]: 
                value
    2009-12-10     99
    2009-12-11     70
    2009-12-12     83
    2009-12-13     90
    2009-12-14     60
    2009-12-15     64
    2009-12-16     59
    2009-12-17     97
    [8 rows x 1 columns]

Postscriptum: a simpler way of creating the dataframe

An index of a range of dates can also be created like this with pandas:

pd.date_range('20091201', periods=31)

Hence the dataframe:

df=pd.DataFrame(np.random.randint(50,100,31), index=pd.date_range('20091201', periods=31))