CODEWITHSUNDEEP
python
nipy
nipy

Reputation: 5488

Filter list of string dates for specific day of week

Given a list containing dates as part of a string:

['2021/08/01/EUR_USD.json',
 '2021/08/02/EUR_USD.json',
 '2021/08/03/EUR_USD.json',
 '2021/08/04/EUR_USD.json',
 '2021/08/05/EUR_USD.json',
 '2021/08/06/EUR_USD.json',
 '2021/08/08/EUR_USD.json',
 '2021/08/09/EUR_USD.json',
 '2021/08/10/EUR_USD.json',
 '2021/08/11/EUR_USD.json',
 '2021/08/12/EUR_USD.json',
 '2021/08/13/EUR_USD.json',
 '2021/08/15/EUR_USD.json']

I want to filter and return only the date and only for Sundays.

This can be done with a list comprehension as follows but I would be interested in other ways of doing this:

def dayOfWeek(l):
    subset = ['/'.join(i.split("/")[0:3])
         for i in l 
             if datetime.strptime('/'.join(
                 i.split("/")[0:3]),'%Y/%m/%d' ).weekday()  == 6 ]
    return subset

['2021-08-01', '2021-08-08', '2021-08-15']

Upvotes: 1

Views: 294

Answers (2)

Ajax1234
Ajax1234

Reputation: 71451

You can use the calendar module with an assignment expression for a shorter comprehension:

import calendar as cl, re
l = ['2021/08/01/EUR_USD.json', '2021/08/02/EUR_USD.json', '2021/08/03/EUR_USD.json', '2021/08/04/EUR_USD.json', '2021/08/05/EUR_USD.json', '2021/08/06/EUR_USD.json', '2021/08/08/EUR_USD.json', '2021/08/09/EUR_USD.json', '2021/08/10/EUR_USD.json', '2021/08/11/EUR_USD.json', '2021/08/12/EUR_USD.json', '2021/08/13/EUR_USD.json', '2021/08/15/EUR_USD.json']
r = ['-'.join(d) for i in l if cl.weekday(*map(int, (d:=re.findall('\d+', i)))) == 6]

Output:

['2021-08-01', '2021-08-08', '2021-08-15']

Upvotes: 2

ThePyGuy
ThePyGuy

Reputation: 18416

List-comprehension is fine, but another way is to use filter builtin

list(filter(lambda x:datetime.strptime(x.rsplit('/', 1)[0], '%Y/%m/%d').weekday()==6, l))

['2021/08/01/EUR_USD.json', '2021/08/08/EUR_USD.json', '2021/08/15/EUR_USD.json']

There are other things you can do:

  1. Instead of splitting and joining the strings, you can use rsplit, with maxsplit=1, then take the first item after the split
  2. You are unnecessarily converting / delimited date string to - delimited date string by
    '-'.join(i.split("/")[0:3]),'%Y-%m-%d' ) which is useless

Upvotes: 2

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