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
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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