通常我们使用 list.Distinc()的时候，默认的是使用 public static IEnumerable<TSource> Distinct<TSource>(this IEnumerable<TSource> source);该方法，但是这样去重的话，是根据每个对象的是否相同来去重，没法达到根据某个对象的属性来去重。
如果想根据某个属性来去重的话，就需要拓展一下 public static IEnumerable<TSource> Distinct<TSource>(this IEnumerable<TSource> source,IEqualityComparer<TSource> comparer);
如下代码。
拓展类：
public class MyEqualityComparer<T,V> : IEqualityComparer<T>
{
private Func<T, V> keyFunc;
private IEqualityComparer<V> comparer;
public MyEqualityComparer(Func<T, V> keyFunc, IEqualityComparer<V> comparer)
{
this.keyFunc = keyFunc;
this.comparer = comparer;
}
public MyEqualityComparer(Func<T, V> keyFunc)
: this(keyFunc, EqualityComparer<V>.Default)
{
}
public bool Equals(T x, T y)
{
return comparer.Equals(keyFunc(x), keyFunc(y));
}
public int GetHashCode(T obj)
{
return comparer.GetHashCode(keyFunc(obj));
}
}
拓展方法：
public static class ExtensionsMethod
{
/// <summary>
/// 拓展distinct
/// </summary>
/// <typeparam name="T">源类型</typeparam>
/// <typeparam name="V">委托返回类型（根据V类型，排除重复项）</typeparam>
/// <param name="source">拓展源</param>
/// <param name="func">委托（执行操作）</param>
/// <returns></returns>
public static IEnumerable<T> Distinct<T, V>(this IEnumerable<T> source, Func<T, V> func)
{
return source.Distinct(new MyEqualityComparer<T, V>(func));
}
}
方法使用：
#region List Distinct 去重
var list=new List<Student>()
{
new Student(){Age = "18",Name = "zhangsan"},
new Student(){Age = "18",Name = "lisi"},
new Student(){Age = "19",Name = "zhangsan"},
};
var listDistinct = list.Distinct();
var listMyDistinct = list.Distinct(c => new {c.Name}).ToList();
#endregion
有个集合，我们想把几个lambda表达式合并起来使用的话，这个方法就很有用
如下代码：
System.Linq.Expressions.Expression<Func<string, bool>> pre = s => false;
System.Linq.Expressions.Expression<Func<string, bool>> expression = e => false;
expression.And(c => c != "");
List<string> preList = new List<string>()
{
"huage",
"zhangsan",
"lisi",
"wangwu",
"zhaolu",
"tianqi"
};
preList.Remove(null);
preList.Remove("huage");
if (preList.Contains("zhangsan"))
{
pre = pre.Or(c => c.Contains("zhangsan"));
}
if (preList.Contains("wangwu"))
{
pre = pre.Or(c => c.Contains("wangwu"));
}
var listStra = preList.Where(pre.Compile()).ToList();
常用的拓展方法
public static class ExtensionsMethod
{
public static Expression<Func<T, bool>> True<T>() { return f => true; }
public static Expression<Func<T, bool>> False<T>() { return f => false; }
public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> expression1,
Expression<Func<T, bool>> expression2)
{
var invokedExpression = Expression.Invoke(expression2, expression1.Parameters
.Cast<Expression>());
return Expression.Lambda<Func<T, bool>>(Expression.Or(expression1.Body, invokedExpression),
expression1.Parameters);
}
public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> expression1,
Expression<Func<T, bool>> expression2)
{
var invokedExpression = Expression.Invoke(expression2, expression1.Parameters
.Cast<Expression>());
return Expression.Lambda<Func<T, bool>>(Expression.And(expression1.Body,
invokedExpression), expression1.Parameters);
}
}
原文：https://www.cnblogs.com/huage-1234/p/12856218.html