对二维数组的列求和 [英] Sum columns of a 2D array

问题描述

我有一个 IEnumerable<IEnumerable<double>> 它基本上可以被认为是一个二维数组，我想做的是得到一个一维数组(或列表或其他)这是我原始收藏的所有列的总数.换句话说，如果我有:

I have an IEnumerable<IEnumerable<double>> which can basically be thought of as a 2D array of doubles and what I want to do is get a 1D array (or list or whatever) that is the total for all the columns of my original collection. In other words, if I had:

1   2   3   4
2   3   1   6
3   4   5   6
-------------
6   9   9   16

我想要最后一行(显然，这不是原始集合的一部分).

I'd want the last line (which is not part of the original collection, obviously).

有没有一种简单的方法可以使用 LINQ 来完成此操作，这样我就不必遍历整个事情了?我知道我可以使用 .Sum 合计一行或一列，但我想合计每一行.

Is there a simple way to do this with LINQ so that I don't have to loop over the whole thing? I know I can use .Sum to total one row or one column, but I want to total each row.

我看到了一些建议使用 group 的其他问题(主要是处理数据库查询)，但这似乎对我不起作用.我试过这个:

I've seen some other questions (mostly dealing with database queries) that suggest using group but that didn't seem to work for me. I tried this:

            var totals = from p in toTotal
                         group p by 1 into g
                         select g.Sum(t => t.First()); 

但这只是全部.

有没有聪明的方法来做到这一点?

Is there a clever way to do this?

例如，如果 toTotal 被定义为:

for example, if toTotal was defined as:

    List<List<double>> toTotal = new List<List<double>>() {
        new List<double> {1,   2,   3,   4},
        new List<double> {2,   3 ,  1,   6},
        new List<double> {3 ,  4,   5 ,  6}
    };

推荐答案

好的.我想我已经成功了:

Ok. I think I've hit on it:

var totals = toTotal.Aggregate((prev, next) => prev.Zip(next, (a, b) => a + b));

诀窍是我一直在寻找 Fold(或 Reduce)函数，但在 LINQ 中它被称为 Aggregate.

The trick was that I was looking for a Fold (or Reduce) function, but in LINQ it's called Aggregate.

这里有一个 fiddle 显示了这个和@Habib 的总行代码(用于比较).与我在这里(以及我在实际代码中使用的)的唯一变化是我需要 .ToList .Zip 的结果，因为对于这个测试用例我有一个 List<List<double>> 如果您没有明确转换为列表，这似乎会让编译器感到不安.在我的实际代码中， toTotal 是一个 IEnumerable 并且不需要转换.

Here's a fiddle showing this and @Habib's code for totaling rows (for comparison). The only change from what I have here (and what I was using in my actual code) is that I needed to .ToList the result of .Zip because for this test case I have a List<List<double>> and that seems to upset the compiler if you don't explicitly convert to a list. In my actual code toTotal is an IEnumerable<IEnumerable<double>> and doesn't need converting.

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