如何检查列表中的所有元素是否都符合条件? [英] How to check if all elements of a list match a condition?

问题描述

我有一个包含20000个列表的列表.我将每个列表的第3个元素用作标志.只要至少一个元素的标志为0，我想对此列表进行一些操作，就像:

I have a list consisting of like 20000 lists. I use each list's 3rd element as a flag. I want to do some operations on this list as long as at least one element's flag is 0, it's like:

my_list = [["a", "b", 0], ["c", "d", 0], ["e", "f", 0], .....]

开头，所有标志均为0.我使用while循环检查至少一个元素的标志是否为0:

In the beginning, all flags are 0. I use a while loop to check if at least one element's flag is 0:

def check(list_):
    for item in list_:
        if item[2] == 0:
            return True
    return False

如果 check(my_list)返回 True ，则我将继续处理列表:

If check(my_list) returns True, then I continue working on my list:

while check(my_list):
    for item in my_list:
        if condition:
            item[2] = 1
        else:
            do_sth()

实际上，我想在my_list上进行迭代时删除其中的一个元素，但是当我对其进行迭代时，不允许删除项目.

Actually, I wanted to remove an element in my_list as I iterated over it, but I'm not allowed to remove items as I iterate over it.

原始my_list没有标志:

Original my_list didn't have flags:

my_list = [["a", "b"], ["c", "d"], ["e", "f"], .....]

由于在迭代过程中无法删除元素，因此发明了这些标志.但是 my_list 包含许多项，而 while 循环会在每个 for 循环中读取所有这些项，这会花费大量时间！你有什么建议吗?

Since I couldn't remove elements as I iterated over it, I invented these flags. But the my_list contains many items, and while loop reads all of them at each for loop, and it consumes lots of time! Do you have any suggestions?

推荐答案

最好的答案是使用生成器表达式结合使用，以产生干净而有效的结果.例如:

The best answer here is to use all(), which is the builtin for this situation. We combine this with a generator expression to produce the result you want cleanly and efficiently. For example:

>>> items = [[1, 2, 0], [1, 2, 0], [1, 2, 0]]
>>> all(flag == 0 for (_, _, flag) in items)
True
>>> items = [[1, 2, 0], [1, 2, 1], [1, 2, 0]]
>>> all(flag == 0 for (_, _, flag) in items)
False

请注意， all(项目中的(_，_，flag)的标志== 0)直接等效于 all(项目中的项目的item [2] == 0)，在这种情况下，阅读起来会更好一些.

Note that all(flag == 0 for (_, _, flag) in items) is directly equivalent to all(item[2] == 0 for item in items), it's just a little nicer to read in this case.

对于过滤器示例，使用列表理解(当然，您可以在适当的地方使用生成器表达式):

And, for the filter example, a list comprehension (of course, you could use a generator expression where appropriate):

>>> [x for x in items if x[2] == 0]
[[1, 2, 0], [1, 2, 0]]

如果要检查至少一个元素为0，则更好的选择是使用 any() 更具可读性:

If you want to check at least one element is 0, the better option is to use any() which is more readable:

>>> any(flag == 0 for (_, _, flag) in items)
True

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