CODEWITHSUNDEEP
python-3.xlistsortingdate
gRoovY_panda
gRoovY_panda

Reputation: 21

Sorting a list of dates

I'm trying to sort a list of given type on the basis of the date

data = [('Anil Kumar', '18-08-2001'), ('Ajay Shastri', '18-08-2000'), ('Sumita Singh', '12-11-1885'), ('Rajni Patel', '11-01-1886'), ('Arshad Khan', '12-11-1887'), ('Christopher Diaz', '19-11-2005'), ('Abha Reddy', '01-01-2005')]

For that I am using map and lambda function

for k in range(len(data)):

         finaldata = list(sorted(data[k][1], key=lambda d: map(int, d.split('-'))))

But I am getting this error

TypeError: '<' not supported between instances of 'map' and 'map'

Upvotes: 0

Views: 58

Answers (2)

Patrick Artner
Patrick Artner

Reputation: 51643

Converting dates to datetimes would be the preferred way to do this, but you can also use number sorting or lexicographical sorting:

data = [('Anil Kumar', '18-08-2001'), ('Ajay Shastri', '18-08-2000'), 
        ('Sumita Singh', '12-11-1885'), ('Rajni Patel', '11-01-1886'), 
        ('Arshad Khan', '12-11-1887'), ('Christopher Diaz', '19-11-2005'), 
        ('Abha Reddy', '01-01-2005')]

# integer sorting
finaldata = sorted(data, key=lambda d: list(reversed(list(map(int, d[1].split('-')))))) 

# lexicograph sorting
finaldata = sorted(data, key=lambda d: list(reversed(d[1].split('-')))) 

print(finaldata)

to get:

[('Sumita Singh', '12-11-1885'), ('Rajni Patel', '11-01-1886'), 
 ('Arshad Khan', '12-11-1887'), ('Ajay Shastri', '18-08-2000'), 
 ('Anil Kumar', '18-08-2001'), ('Abha Reddy', '01-01-2005'), 
 ('Christopher Diaz', '19-11-2005')]

To additionall sort by the name you need to sort with a key of (date,name), you can do this using:

finaldata = sorted(data, 
                   key = lambda d: (list(reversed(list(map(int, d[1].split('-'))))), 
                                    d[0]))

Upvotes: 1

RoadRunner
RoadRunner

Reputation: 26315

Since map() returns an iterator, you cannot use it like that in a comparison function, since you cannot do equality comparisons with two map objects. Even if you cast to a list or another collection, there are still many other problems with your code, as highlighted in @Patrick Artner's comment.

Instead you should use datetime.datetime.strptime to convert the date strings to datetime objects for the comparison key function.

The time format "%d-%m-%Y" is good enough here, where %d is zero padded days, %m is zero padded months, and %Y is years with century numbers included. You can refer to the strftime() and strptime() Format Codes from the documentation for further reading.

Demo

from datetime import datetime

data = [('Anil Kumar', '18-08-2001'), ('Ajay Shastri', '18-08-2000'), ('Sumita Singh', '12-11-1885'), ('Rajni Patel', '11-01-1886'), ('Arshad Khan', '12-11-1887'), ('Christopher Diaz', '19-11-2005'), ('Abha Reddy', '01-01-2005')]

print(sorted(data, key=lambda d: datetime.strptime(d[1], "%d-%m-%Y")))

Output:

[('Sumita Singh', '12-11-1885'), ('Rajni Patel', '11-01-1886'), ('Arshad Khan', '12-11-1887'), ('Ajay Shastri', '18-08-2000'), ('Anil Kumar', '18-08-2001'), ('Abha Reddy', '01-01-2005'), ('Christopher Diaz', '19-11-2005')]

Upvotes: 1

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