展平列表列表 [英] Flatten list of lists

问题描述

我在 Python 中遇到方括号问题.我写了一个产生以下输出的代码:

[[180.0], [173.8], [164.2], [156.5], [147.2], [138.2]]

但我想用它进行一些计算，但方括号不允许我这样做.

如何去掉括号?我看到了一些例子来做到这一点，但我无法将它们应用到这个案例中.

解决方案

使用嵌套列表推导式将列表展平以去除括号".这将取消嵌套列表中存储的每个列表！

list_of_lists = [[180.0], [173.8], [164.2], [156.5], [147.2], [138.2]]flattened = [val for sublist in list_of_lists for val in sublist]

嵌套列表推导式的计算方式与它们展开的方式相同(即为每个新循环添加换行符和制表符.因此在这种情况下:

flattened = [val for sublist in list_of_lists for val in sublist]

相当于:

扁平化 = []对于 list_of_lists 中的子列表:对于子列表中的 val:flattened.append(val)

最大的不同在于，list comp 的计算速度比 unraveled 循环快得多，并且消除了 append 调用！

如果您在子列表中有多个项目，则列表组合甚至会将其展平.即

<预><代码>>>>list_of_lists = [[180.0, 1, 2, 3], [173.8], [164.2], [156.5], [147.2], [138.2]]>>>flattened = [val for sublist in list_of_lists for val in sublist]>>>压扁的[180.0, 1, 2, 3, 173.8, 164.2, 156.5, 147.2,138.2]

I'm having a problem with square brackets in Python. I wrote a code that produces the following output:

[[180.0], [173.8], [164.2], [156.5], [147.2], [138.2]]

But I would like to perform some calculations with that, but the the square brackets won't let me.

How can I remove the brackets? I saw some examples to do that but I could not apply them to this case.

解决方案

Flatten the list to "remove the brackets" using a nested list comprehension. This will un-nest each list stored in your list of lists!

list_of_lists = [[180.0], [173.8], [164.2], [156.5], [147.2], [138.2]]
flattened = [val for sublist in list_of_lists for val in sublist]

Nested list comprehensions evaluate in the same manner that they unwrap (i.e. add newline and tab for each new loop. So in this case:

flattened = [val for sublist in list_of_lists for val in sublist]

is equivalent to:

flattened = []
for sublist in list_of_lists:
    for val in sublist:
        flattened.append(val)

The big difference is that the list comp evaluates MUCH faster than the unraveled loop and eliminates the append calls!

If you have multiple items in a sublist the list comp will even flatten that. ie

>>> list_of_lists = [[180.0, 1, 2, 3], [173.8], [164.2], [156.5], [147.2], [138.2]]
>>> flattened  = [val for sublist in list_of_lists for val in sublist]
>>> flattened 
[180.0, 1, 2, 3, 173.8, 164.2, 156.5, 147.2,138.2]

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