具有多个属性和混合顺序的列表排序 [英] List sorting with multiple attributes and mixed order

问题描述

我必须对具有多个属性的列表进行排序.我可以轻松地按升序对所有属性进行此操作

I have to sort a list with multiple attributes. I can do that in ascending order for ALL attributes easily with

L.sort(key=operator.attrgetter(attribute))....

但是问题是，我必须使用混合配置进行升序/降序...我必须模仿" SQL Order By，在其中可以执行类似name ASC, year DESC的操作. 有没有一种方法可以在Python中轻松实现，而无需实现自定义比较功能?

but the problem is, that I have to use mixed configurations for ascending/descending... I have to "imitate" a bit the SQL Order By where you can do something like name ASC, year DESC. Is there a way to do this easily in Python without having to implement a custom compare function?

推荐答案

如果您的属性是数字属性，那么您就有了.

If your attributes are numeric, you have this.

def mixed_order( a ):
    return ( a.attribute1, -a.attribute2 )

someList.sort( key=mixed_order )

如果您的属性包含字符串或其他更复杂的对象，则可以选择.

If your attributes includes strings or other more complex objects, you have some choices.

.sort()方法很稳定:您可以进行多次遍历.这也许是最简单的.它也非常快.

The .sort() method is stable: you can do multiple passes. This is perhaps the simplest. It's also remarkably fast.

def key1( a ): return a.attribute1
def key2( a ): return a.attribute2

someList.sort( key=key2, reverse=True )
someList.sort( key=key1 )

如果这是唯一的排序，则可以定义自己的专用比较运算符.最少需要__eq__和__lt__.其他四个可以通过简单的逻辑从这两个派生.

If this is the only sort, you can define your own special-purpose comparison operators. Minimally, you need __eq__ and __lt__. The other four can be derived from these two by simple logic.

这篇关于具有多个属性和混合顺序的列表排序的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！