CODEWITHSUNDEEP
pythondatetime
Zanam
Zanam

Reputation: 4807

Python obtaining list of first days in a month from list of datetime

I have a list 'A' the contents of which is datetime.datetime.

I want to obtain another list or array 'B' which stores the first day of month for each of the datetime in the list A.

I want to obtain another list or array 'C' which stores just the month number for each datetime in A.

Is it possible to achieve this in a smarter way other than using a for loop. I have grandfathered the code but I am at liberty to change the A, B, C into list or arrays, etc as it suits me.

date_format     =   "%m/%d/%Y"
st_dt   =   datetime.strptime( '02/01/2016', date_format )
en_dt   =   datetime.strptime( '03/31/2016', date_format )
A = [ st_dt + timedelta( days = x ) for x in range( ( en_dt - st_dt ).days + 1 ) ]

Edit: First day means First date e.g. if the date is 2/15/2016 then first date for my case would be 2/1/2016

Upvotes: 0

Views: 351

Answers (1)

eumiro
eumiro

Reputation: 213125

Using pandas:

dts = [datetime(2016,2,1), datetime(2016,3,31)]

import pandas as pd

a = pd.DatetimeIndex(dts)

# a: <class 'pandas.tseries.index.DatetimeIndex'>
#    [2016-02-01, 2016-03-31]
#    Length: 2, Freq: None, Timezone: None


# b stores the first day of month for each of the datetime in the list a.

b = a.map(lambda x: x.replace(day=1))

# b: array([Timestamp('2016-02-01 00:00:00'),
#           Timestamp('2016-03-01 00:00:00')], dtype=object)


# c stores just the month number for each datetime in a.

c = a.month

# c: array([2, 3], dtype=int32)

Upvotes: 1

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