30秒学会 C# 片段 – DifferenceBy

Returns the difference between two collections, after applying the provided function to each element of both.

Use IEnumerable.Select() to map each element of either collection to the desired type.
Use IEnumerable.Except() to only return elements in the second enumerable object and not the first one.

代码实现

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

public static partial class _30s 
{
  public static IEnumerable<R> DifferenceBy<T,R>(IEnumerable<T> a, IEnumerable<T> b, Func<T,R> map)
  {
    return a.Select(map).Except(b.Select(map));
  }
}

使用样例

var p = new[] {
  new { a = 3, b = 2},
  new { a = 2, b = 1}
};
var q = new[] {
  new { a = 6, b = 2}
};

_30s.DifferenceBy(p, q, x => x.b); // { 1 }