[英]Apply a function to every item of an arbitrarily nested list
I have a nested list a = [1, 2, [3, 4], 5]
and I want to apply a function that will raise every number to the power of 2. The result will be like this:我有一个嵌套列表
a = [1, 2, [3, 4], 5]
我想应用一个函数,将每个数字提高到 2 的幂。结果将是这样的:
a = [1, 4, [9, 16], 25]
I tried a = [list(map(lambda x: x * x, x)) for x in a]
but it gives this error我尝试
a = [list(map(lambda x: x * x, x)) for x in a]
但它给出了这个错误
'int' object is not iterable
How we can fix this issue?我们如何解决这个问题? How can I apply a function over a nested list?
如何在嵌套列表上应用函数?
You probably need a recursive function that distinguishes between lists and scalars:您可能需要一个区分列表和标量的递归函数:
def square(item):
if isinstance(item, list):
return [square(x) for x in item]
else:
return item * item
square(a)
#[1, 4, [9, 16], 25]
Incidentally, this approach works for arbitrary-nested lists.顺便说一下,这种方法适用于任意嵌套列表。
Here's a more general solution:这是一个更通用的解决方案:
def apply(item, fun):
if isinstance(item, list):
return [apply(x, fun) for x in item]
else:
return fun(item)
apply(a, lambda x: x * x)
#[1, 4, [9, 16], 25]
You are decomposing your list into its elements -some of them are lists which can not be multiplied with itself ( [3,4]*[3,4]
).您正在将列表分解为其元素 - 其中一些是不能与自身相乘的列表(
[3,4]*[3,4]
)。
Not sure if that is smart - but you can use a "recursing" lambda:不确定这是否明智——但您可以使用“递归”lambda:
a =[1, 2, [3, 4], 5]
l = lambda x : x * x if isinstance(x,int) else list(map(l,x))
a = list(map(l, a))
print(a)
Output:输出:
[1, 4, [9, 16], 25]
Works also for "deeper" levels:也适用于“更深层次”的水平:
a =[1, 2, [3, [7,8], 4], 5]
Output:输出:
[1, 4, [9, [49, 64], 16], 25]
but will crash if you mix non-iterables things into the mix但如果你将不可迭代的东西混入其中会崩溃
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