Python3 asc desc排序

Question

Lets assume I've got a following python list(this is only example):

my_list = [{'user': 'Joe', 'score': 14},
           {'user': 'Foo', 'score': 12},
           {'user': 'May', 'score': 12},
           {'user': 'Kat', 'score': 12},
           {'user': 'Doe', 'score': 13}]

I need to sort this list in ascending order by score and descending order by a username. Expected sort result:

my_list = [{'user': 'May', 'score': 12},
           {'user': 'Kat', 'score': 12},
           {'user': 'Foo', 'score': 12},
           {'user': 'Doe', 'score': 13},
           {'user': 'Joe', 'score': 14}]

So, I could do something like this if I want everything to be in ascending order:

my_list.sort(key=lambda x: (x['score'], x['user']))

For integers it is easy to solve this problem just adding - in front of it:

my_list.sort(key=lambda x: (-x['score'], x['user']))

Unfortunately, strings can not be negative :-|

I need a generic solution that doesn't involve 'reverse=True'. Lambda function is dynamically generated based on a user config.

Thoughts?

Answer 1

Your current solution will work fine if you set the reverse parameter of list.sort to True :

>>> my_list = [{'user': 'Joe', 'score': 14},
...            {'user': 'Foo', 'score': 12},
...            {'user': 'May', 'score': 12},
...            {'user': 'Kat', 'score': 12},
...            {'user': 'Doe', 'score': 13}]
>>> my_list.sort(key=lambda x: (-x['score'], x['user']), reverse=True)
>>> pprint(my_list) # pprint makes the nice output
[{'score': 12, 'user': 'May'},
 {'score': 12, 'user': 'Kat'},
 {'score': 12, 'user': 'Foo'},
 {'score': 13, 'user': 'Doe'},
 {'score': 14, 'user': 'Joe'}]
>>>

This will sort the list in reverse order.

---

Edit:

Since the names and scores have two different sort orders, you will need to use two separate sorts to achieve your desired output:

>>> my_list = [{'user': 'Joe', 'score': 14},
...            {'user': 'Foo', 'score': 12},
...            {'user': 'May', 'score': 12},
...            {'user': 'Kat', 'score': 12},
...            {'user': 'Doe', 'score': 13}]
>>> my_list.sort(key=lambda x: x['user'], reverse=True)
>>> my_list.sort(key=lambda x: x['score'])
>>> pprint(my_list)
[{'score': 12, 'user': 'May'},
 {'score': 12, 'user': 'Kat'},
 {'score': 12, 'user': 'Foo'},
 {'score': 13, 'user': 'Doe'},
 {'score': 14, 'user': 'Joe'}]
>>>

Answer 2

The ord of a string can be negative:

my_list.sort(key=lambda x: (x["score"],[-ord(x) for x in x["user"]])))


In [50]:  my_list.sort(key=lambda x: (x["score"],[-ord(x) for x in x["user"]]))

In [51]: my_list
Out[51]: 
[{'score': 12, 'user': 'May'},
 {'score': 12, 'user': 'Kat'},
 {'score': 12, 'user': 'Foo'},
 {'score': 13, 'user': 'Doe'},
 {'score': 14, 'user': 'Joe'}]

Answer 3

you need to add the reverse=True keyword for descending order.

>>> my_list.sort(key=lambda x: (-x['score'], x['user']),reverse=True)
>>> my_list
[{'score': 12, 'user': 'May'}, {'score': 12, 'user': 'Kat'}, {'score': 12, 'user': 'Foo'}, {'score': 13, 'user': 'Doe'}, {'score': 14, 'user': 'Joe'}]