30秒学会 C# 片段 – AverageBy

Returns the average of a collection, after mapping each element to a value using the provided function.

Use IEnumerable.Select() to map each element to the value returned by the provided selector function, fn.
Use IEnumerable.Average() to get the average of the resulting values.

代码片段

using System.Collections.Generic;
using System.Linq;

public static partial class _30s 
{
  public static double AverageBy<T>(IEnumerable<T> values, Func<T,int> fn) 
  {
    return values.Select(fn).Average();
  }
}

使用样例

var p = new [] {
  new { a = 3, b = 2},
  new { a = 2, b = 1}
};

_30s.AverageBy(p, v => v.a); // 2.5
_30s.AverageBy(p, v => v.b); // 1.5