如何获得符合条件的通用列表元素的平均值? [英] How can I get the average of the elements of a generic list that meet a criteria?
问题描述
我想重新创建excel函数AVERAGEIF的通用版本.定义如下:
I'd like to recreate a generic version of the excel function AVERAGEIF. It is defined as the following:
返回以下范围内所有单元的平均值(算术平均值) 符合给定条件
Returns the average (arithmetic mean) of all the cells in a range that meet a given criteria
我的问题是我不知道如何定义通用平均值函数的类型签名.以下是我拥有的几乎可以正常工作的代码.
My problem is that I don't know how to define the type signature of the generic average function. The following is the almost working code that I have.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace ConsTestApp
{
class Program
{
static void Main(string[] args)
{
var dl = new List<double>() { 10, 10, 0, 0 };
var bl = new List<bool>() { true, true, false, false };
Func<bool, bool> criteria = c => c == true;
Console.Out.WriteLine(AVERAGEIF<double, bool>(dl, bl, criteria));
Console.In.Read();
}
static T1 AVERAGEIF<T1, T2>(List<T1> average_range, List<T2> criteria_range, Func<T2, bool> applyCriteria)
{
var cl1 = new List<Container<T1>>();
foreach (var cl in average_range)
{
cl1.Add(new Container<T1>(cl));
}
var cl2 = new List<Container<T2>>();
foreach (var cl in criteria_range)
{
cl2.Add(new Container<T2>(cl));
}
List<Container<T1>> result =
new List<Container<T1>>((from d in cl1
join b in cl2
on d.Id equals b.Id
where applyCriteria(b.Value)
select new Container<T1> { Value = d.Value, }).ToList<Container<T1>>());
var ret = result.Average<T1>(s => s.Value);
//
// return ret;
return default(T1);
}
}
class Container<T>
{
private static uint count = 0;
public Container()
: base()
{
count++;
this.Id = count;
}
public Container(T t)
: this()
{
this.Value = t;
}
public T Value
{
get;
set;
}
public uint Id
{
get;
private set;
}
}
class ContainerList<T> : List<Container<T>>
{
List<Container<T>> m_list;
public ContainerList()
: base()
{
this.m_list = new List<Container<T>>();
}
public ContainerList(List<T> l)
: this()
{
foreach (var li in l)
{
this.m_list.Add(new Container<T>(li));
}
}
public ContainerList(List<Container<T>> l)
: this()
{
this.m_list = l;
}
public T Average(Func<Container<T>, T> selector)
{
T ret = default(T);
if (typeof(T) == typeof(double))
ret = (T)(object)(double)0.0;
else if (typeof(T) == typeof(decimal))
ret = (T)(object)(decimal)0.0;
else
ret = default(T);
return ret;
}
}
}
推荐答案
我想重新创建excel函数AVERAGEIF的通用版本
I'd like to recreate a generic version of the excel function AVERAGEIF
为什么不只使用LINQ?
Why don't you just use LINQ?
var average = collection.Where(x => x.Something)
.Average(x => x.SomeProperty);
请注意,如果没有匹配的元素,这将引发异常.如果您不想这样做,可以使用:
Note that this will throw an exception if there are no matching elements. If you don't want that, you could use:
var average = collection.Where(x => x.Something)
.DefaultIfEmpty()
.Average(x => x.SomeProperty);
尚不清楚为什么要为此创建单独的方法.
It's not clear why you would want to create a separate method for this.
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