問題描述

我有一個 IEnumerable<IEnumerable<double>> 它基本上可以被認為是一個二維數(shù)組，我想做的是得到一個一維數(shù)組(或列表或其他)這是我原始收藏的所有列的總數(shù).換句話說，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(顯然，這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).

有沒有一種簡單的方法可以使用 LINQ 來完成此操作，這樣我就不必遍歷整個事情了?我知道我可以使用 .Sum 合計一行或一列，但我想合計每一行.

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.

我看到了一些建議使用 group 的其他問題(主要是處理數(shù)據(jù)庫查詢)，但這似乎對我不起作用.我試過這個:

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()); 

但這只是全部.

有沒有聰明的方法來做到這一點?

Is there a clever way to do this?

例如，如果 toTotal 被定義為:

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}
    };

推薦答案

好的.我想我已經(jīng)成功了:

Ok. I think I've hit on it:

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

訣竅是我一直在尋找 Fold(或 Reduce)函數(shù)，但在 LINQ 中它被稱為 Aggregate.

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

這里有一個 fiddle 顯示了這個和@Habib 的總行代碼(用于比較).與我在這里(以及我在實際代碼中使用的)的唯一變化是我需要 .ToList .Zip 的結(jié)果，因為對于這個測試用例我有一個 List<List<double>> 如果您沒有明確轉(zhuǎn)換為列表，這似乎會讓編譯器感到不安.在我的實際代碼中， toTotal 是一個 IEnumerable 并且不需要轉(zhuǎn)換.