C# 使用 LINQ 获取带有自定义对象的列表的总和/平均值
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Using LINQ to Get Sum/ Average of a List with custom objects
提问by Graviton
I have a class:
我有一堂课：
public class PointD
{
public double X
{ get; set; }
public double Y
{ get; set; }
public PointD(double x, double y)
{
X = x;
Y=y;
}
//operator for +,-, * and / are overridden
}
Given a list<PointD>, how to get the average of it using LINQ? A forloop equivalent will be something like this:
给定 a list<PointD>，如何使用 LINQ 获得它的平均值？一个for循环等效将是这样的：
double xx, yy;
for ( int i=0; i< ptlist.Count; i++)
{
xx+=ptlist[i].X;
yy+=ptlist[i].Y;
}
return new PointD(){X=xx, Y=yy};
You can use any built-inLINQ function only. You can't define an extension that takes care of this function.
您只能使用任何内置LINQ 函数。您无法定义负责此功能的扩展。
Any idea?
任何的想法？
Edit: Of course, you can use two separate Sumextension method to Sum for X and Y component before merging them. But this is not what I want. What I want is a single query/ method that does the job
编辑：当然，您可以Sum在合并之前使用两个单独的扩展方法对 X 和 Y 组件进行求和。但这不是我想要的。我想要的是完成这项工作的单个查询/方法
采纳答案by Noldorin
The Aggregatefunction would come in handy here.
这个Aggregate函数在这里会派上用场。
var sum = list.Aggregate((acc, cur) => acc + cur);
var average = list.Aggregate((acc, cur) => acc + cur) / list.Count;
Just insure that you have the /operator defined for types PointDand int, and this should do the job.
只要确保您/为类型PointD和定义了运算符int，这应该可以完成工作。
Note: I'm not quite sure whether you want the sum or average here (your question is somewhat ambiguous about this), but I've included examples for both.
注意：我不太确定您是想要总和还是平均值（您的问题对此有些模棱两可），但我已经包含了两者的示例。
回答by Greg Beech
You'll need to use the Aggregatemethod instead so you can provide your own aggregation function (Sumis just a convenient specialized case of this method). Something like:
您需要改用该Aggregate方法，以便您可以提供自己的聚合函数（Sum只是此方法的一个方便的特例）。就像是：
points.Aggregate(new PointD(0, 0), (a, p) => a + p);
I know you say you don't want any additional methods defined, but if this is a common operation I'd be inclined to write an extension method for this, i.e.
我知道你说你不想定义任何额外的方法，但如果这是一个常见的操作，我倾向于为此编写一个扩展方法，即
public static PointD Sum(this IEnumerable<PointD> source)
{
return source.Aggregate(new PointD(0, 0), (a, p) => a + p);
}
Because it's much more readable to be able to write:
因为能够编写更具可读性：
points.Sum();
回答by Ruben Bartelink
[Fact]
public void CanAddManyPointDs()
{
var points = new[]{
new PointD( 1,1),
new PointD( 2,3),
new PointD( 3,4),
};
var result = points.Aggregate((p1, p2) => new PointD(p1.X + p2.X, p1.Y + p2.Y));
Assert.Equal(result.X,6);
Assert.Equal(result.Y,8);
}
