python获取列表并仅在使用set也存在负值时才返回
问题描述
基本上我有一个很大的清单:
Basically I have a big list:
# where (n) is over a couple hundred thousand or is 1 million
def big_list(n):
return [ randrange(-n//3,n//3) for i in range(n) ]
并且使用 set 当且仅当它的负值也存在时，我必须返回一个新列表.
And using a set I must return a new list if and only if its negative value also exists.
例如.如果 list = [-3,-2,-1,2,1,4]它应该返回 new_list = [2,1]
Ex. if list = [-3,-2,-1,2,1,4]
it should return new_list = [2,1]
我必须使用 set 来完成这项工作，我真的迷路了.
I must do this using set, and I''m really lost.
解决方案
如果您从使用 big_list() 创建的列表中创建 set，则可以使用它来通过遍历集合的所有元素并选择所有值大于 0 且负值也在集合中的元素来创建所需的结果列表.
If you create a set from a list created with big_list(), you can use it to create a desired result list by iterating through all the elements of the set and selecting all those whose values are > 0 and whose negative value is also in the set.
您可以使用列表显示表达式，通常称为列表推导式"，用于在 [] 括号内创建带有一行长代码的结果列表，就像 big_list() 函数一样.
You can use a list display expression, commonly call a "list comprehension", to create the resultant list with one long-ish line of code inside [] brackets, like the big_list() function does.
希望这会有所帮助.
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