2D阵列的总和列 [英] Sum columns of a 2D array

问题描述

我有一个IEnumerable<IEnumerable<double>>，它基本上可以看作是2D的双精度数组，而我想做的就是得到一个1D数组(或列表或其他东西)，该数组是原始集合中所有列的总和.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).

是否有使用LINQ做到这一点的简单方法，这样我就不必遍历整个事情了?我知道我可以使用.Sum总计一行或一列，但是我想总计每一行.

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.

我已经看到其他一些建议使用group的问题(主要是处理数据库查询)，但这似乎对我不起作用.我试过了:

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()); 

但这只是全部内容.

有聪明的方法吗?

例如，如果toTotal被定义为:

    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.我想我已经做到了:

Ok. I think I've hit on it:

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

诀窍是我正在寻找Fold(或Reduce)函数，但是在LINQ中它称为Aggregate.

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

这是一个小提琴，其中显示了此代码以及@Habib的用于总计行的代码(以进行比较).与此处(以及我在实际代码中使用的内容)相比，唯一的变化是我需要对.Zip的结果进行.ToList，因为对于此测试用例，我有一个List<List<double>>，这似乎使如果您未明确转换为列表，则为编译器.在我的实际代码中，toTotal是IEnumerable<IEnumerable<double>>，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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