使用函数在指定索引处开始Python中不同长度的列表 [英] Summing lists of different lengths in Python beginning at a specified index using a function

问题描述

如何将多个列表从列表中的指定索引开始组合起来，同时也将各个索引的值相加？

How can I combine multiple lists starting at a specified index within one of the lists, while also summing the values at the respective indexes?

如果我有3个列表：

If I had 3 lists:

a = [1, 2, 3, 4, 5, 0, 0, 0, 0]
b = [2, 3, 4, 5, 6]
c = [5, 2]

我怎么做到这一点，以便我可以在 b 和 c 列表> a ，并且各个指标会相加？

How could I make it so that I could insert lists b and c into any position within a, and the respective indexes would sum?

例如，我可以从的第一个索引开始插入 b / code>，并从 a 的第五个索引开始插入 c 列表。这样的输出看起来像这样：



For example, I could insert list b starting from the first index of a, and also insert list c starting from the fifth index of a. The output of this would look something like:

NewList = [1, 4, 6, 8, 10, *11*, 2, 0, 0]

您可以看到，当添加列表 b 和 c 在上述 a 的索引处，第五个索引处出现重叠，我想这样做。

You can see that when adding lists b and c at the aforementioned indexes of a, there was an overlap at the fifth index, which I would like to do.

我已经尝试从 itertools使用 izip_longest code>结合切片方法：



I have tried using izip_longest from itertools in combination with a slicing method:

result = [sum(n) for n in izip_longest(a[2:], b, fillvalue=0)]  

但是这会产生：

result = [5, 7, 9, 5, 6, 0, 0]

这会切断列表 a 中的零和一个索引，这是我不想要的。但是，我想使用 izip_longest ，因为我可以对不同长度的列表进行求和。

This cuts off the zero and one index in list a, which I do not want. However, I want to use izip_longest because I can sum lists with different lengths.

我想创建一个可以用任意数量的列表执行此操作的函数，因此 a 可能是一个列表中有len = 1000，我可以根据需要插入任意数量的不同长度的不同长度的列表，这些列表可以是任何我想要的 a ，并且索引值可以相加。 / b>

I would like to create a function that does this with an arbitrary amount of lists, so a could be a list with len = 1000 and I could insert any amount of different lists with different lengths wherever I want into a, as many times as I want and the index values would sum.

推荐答案

这是一个应该做你要求的功能：

Here is a function that should do what you're asking for:

def combine(lista, listb, index_in_list_a_to_start_insert):
    # left pad list b with zeros
    newb = [0]*index_in_list_a_to_start_insert + listb

    # right pad shorter list
    max_len = max(len(lista), len(newb))
    newa = lista if len(lista) >= max_len else lista + [0]*(max_len-len(lista))
    newb = newb if len(newb) >= max_len else newb + [0]*(max_len-len(newb))

    # sum element-wise            
    return [a + b for a, b in zip(newa,newb)]

You can run your example by chaining this function as so:

a = [1, 2, 3, 4, 5, 0, 0, 0, 0]
b = [2, 3, 4, 5, 6]
c = [5, 2]
combine(combine(a, b, 1), c, 5)

输出：

Output:

 [1, 4, 6, 8, 10, 11, 2, 0, 0]

您可能还想添加一些错误检查以确保指定的索引处于界限内。

You'd probably also want to add some error checking to make sure that the specified index is in-bounds.

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