Python:如何在数字初级排序中执行二级降序字母排序

Question

在Sorting a Python list by two criteria Fouad 给出了如下答案:

sorted(list, key=lambda x: (x[0], -x[1]))

我想主要对元组列表中的以下列表进行排序，主要对每个元素中的第二个项目按升序排序，然后是第一个(字母)项目按降序排序:

[('Ayoz', 1, 18, 7), ('Aidan', 2, 4, 9), ('Alan', 2, 4, 9), ('Arlan', 5, 6, 7), ('Luke', 15, 16, 2), ('Tariq', 5, 4, 2)] 

给出答案:

[('Ayoz', 1, 18, 7), ('Alan', 2, 4, 9), ('Aidan', 2, 4, 9), ('Tariq', 5, 4, 2), ('Arlan', 5, 6, 7), ('Luke', 15, 16, 2)]

如果可能，使用上述方法。我试过了

tlist = [('Ayoz', 1, 18, 7), ('Aidan', 2, 4, 9), ('Alan', 2, 4, 9), ('Arlan', 5, 6, 7), ('Luke', 15, 16, 2), ('Tariq', 5, 4, 2)]
sorted(tlist, key=lambda elem: (elem[1], -elem[0]))

但这仅在 elem[0] 为数字时有效(在这种情况下它会给出 TypeError: bad operand type for unary -: 'str')

如有任何帮助，我将不胜感激。 Python版本为3.4

Answer 1

Python 中内置的排序例程是稳定的。也就是说，如果两个项目具有相同的键值，那么它们将保持彼此之间的顺序(靠近列表前面的那个仍然靠近前面)。因此，您可以使用多个排序 channel 对多个键进行排序。

from operator import itemgetter

tlist = [('Ayoz', 1, 18, 7), ('Aidan', 2, 4, 9), ('Alan', 2, 4, 9),
         ('Arlan', 5, 6, 7), ('Luke', 15, 16, 2), ('Tariq', 5, 4, 2)]

# sort by name in descending order
tlist.sort(key=itemgetter(0), reverse=True) 
print('pass 1:', tlist)

# sort by element 1 in ascending order.  If two items have the same value
# the names stay in the same order they had (descending order)
tlist.sort(key=itemgetter(1))
print(npass 2:', tlist)

打印:

pass 1: [('Tariq', 5, 4, 2), ('Luke', 15, 16, 2), ('Ayoz', 1, 18, 7), ('Arlan', 5, 6, 7), ('Alan', 2, 4, 9), ('Aidan', 2, 4, 9)]

pass 2: [('Ayoz', 1, 18, 7), ('Alan', 2, 4, 9), ('Aidan', 2, 4, 9), ('Tariq', 5, 4, 2), ('Arlan', 5, 6, 7), ('Luke', 15, 16, 2)]