Python:如何从列表中删除/删除第n个元素? [英] Python: how to remove/delete every n-th element from list?

问题描述

我已经看过这篇文章: Python:从现有的列表中构建新列表删除每个第n个元素，但由于某种原因，它对我不起作用:

我尝试过这种方式:

def drop(mylist, n):
    del mylist[0::n]
    print(mylist)

此功能获取一个列表和一个n.然后，它使用列表中的n步删除每个第n个元素，并打印结果.

这是我的函数调用:

drop([1,2,3,4],2)

错误的输出:
[2, 4]代替[1, 3]

---

然后我尝试了上面链接中的一种变体:

def drop(mylist, n):
    new_list = [item for index, item in enumerate(mylist) if index % n != 0]
    print(new_list)

再次，函数调用:

drop([1,2,3,4],2)

给我同样的错误结果: [2, 4]代替[1, 3]

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如何从列表中正确删除/删除/删除第n个项目?

解决方案

在您的第一个函数中，mylist[0::n]是[1, 3]，因为0::n表示第一个元素为0，其他元素每第n个 元素在第一个之后.正如Daniel所建议的，您可以使用mylist[::n]，这意味着每第n个 个元素.

在您的第二个函数索引中，索引以0开头，而0 % 0为0，因此它不会复制第一个元素.第三个元素(2 % 2为0)相同.所以您要做的就是new_list = [item for index, item in enumerate(mylist) if (index + 1) % n != 0]

提示:在此类功能中，您可能希望使用return而不是print().

I had already looked through this post: Python: building new list from existing by dropping every n-th element, but for some reason it does not work for me:

I tried this way:

def drop(mylist, n):
    del mylist[0::n]
    print(mylist)

This function takes a list and n. Then it removes every n-th element by using n-step from list and prints result.

Here is my function call:

drop([1,2,3,4],2)

Wrong output:
[2, 4] instead of [1, 3]

---

Then I tried a variant from the link above:

def drop(mylist, n):
    new_list = [item for index, item in enumerate(mylist) if index % n != 0]
    print(new_list)

Again, function call:

drop([1,2,3,4],2)

Gives me the same wrong result: [2, 4] instead of [1, 3]

---

How to correctly remove/delete/drop every n-th item from a list?

解决方案

In your first function mylist[0::n] is [1, 3] because 0::n means first element is 0 and other elements are every nth element after first. As Daniel suggested you could use mylist[::n] which means every nth element.

In your second function index is starting with 0 and 0 % 0 is 0, so it doesn't copy first element. It's same for third element (2 % 2 is 0). So all you need to do is new_list = [item for index, item in enumerate(mylist) if (index + 1) % n != 0]

Tip: you may want to use return instead of print() in functions like these.

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