I am trying to sort a nested list by date (which I can). Then if the list has duplicate dates, sort the duplicate dates by time.
The first part of the list is the date or time, second part is the index.
Same index in both lists means they belong with each other:
[b'05-07-2024', 0]belongs with[b'15-21-00', 0][b'16-08-2024', 1]belongs with[b'23-41-01', 1]
I can sort one of the lists at a time like this:
index_list = []
for _, index in date_list:
index_list.append(index)
The index_list is:
[0, 1, 2]
But index 1 & 2 should actually be swapped in this case because these are the lists:
date_list = [[b'05-07-2024', 0], [b'16-08-2024', 1], [b'16-08-2024', 2]]
time_list = [[b'15-20-55', 2], [b'15-21-00', 0], [b'23-41-01', 1]]
In the end I need a list of the indexes of the right order.
In this case that would be:
[0, 2, 1]
9
Combine date and time into a datetime object, then you can simply sort by it.
from datetime import datetime
sorted_indexes = sorted(
[idx for date, idx in date_list],
key=lambda idx: datetime.strptime(
f"{date_list[idx][0].decode('utf-8')} {next(t[0] for t in time_list if t[1] == idx).decode('utf-8')}",
'%d-%m-%Y %H-%M-%S'
)
)
Output:
[0, 2, 1]
2
If your date strings were in YYYY-MM-DD format and your data was structured like this,
data = [
('2024-07-05', b'15-21-00', 0),
('2024-08-16', b'23-41-01', 1),
('2024-08-16', b'15-20-55', 2)
]
then you could just use the built-in sorted function as-is,
sorted_indexes = [i for date, time, i in sorted(data)]
because sorted sorts lists of tuples lexicographically (i.e., first by date, then equal dates by time, and as a bonus, equal times by index).
Since you don’t have this format and structure, you need to create it (temporarily). You can use a dictionary to combine the corresponding dates and times:
tmp = {}
for date, i in date_list:
tmp[i] = [date]
for time, i in time_list:
tmp[i].append(time) # assuming that i was already contained in date_list
data = [(date, time, i) for i, (date, time) in tmp.items()]
You can use the datetime module to convert each date string:
from datetime import datetime
def convert_date(date):
"""Convert byte string in DD-MM-YYYY to Unicode string in YYYY-MM-DD format."""
return datetime.strptime(date.decode(), "%d-%m-%Y").strftime("%Y-%m-%d")
You can put everything in a function to keep it tidy:
def sort_dates_and_times(dates, times):
tmp = {}
for date, i in dates:
tmp[i] = [convert_date(date)]
for time, i in times:
tmp[i].append(time) # assuming that i was already contained in date_list
data = [(date, time, i) for i, (date, time) in tmp.items()]
return [i for date, time, i in sorted(data)]
sorted_indexes = sort_dates_and_times(date_list, time_list)
4