C#lambda表达式和IComparer
我正在使用lambda表达式对C#中的数组进行排序和搜索。我不想在我的类中实现IComparer接口,因为我需要对多个成员字段进行排序和搜索。C#lambda表达式和IComparer
class Widget
{
public int foo;
public void Bar()
{
Widget[] widgets;
Array.Sort(widgets, (a, b) => a.foo.CompareTo(b.foo));
Widget x = new Widget();
x.foo = 5;
int index = Array.BinarySearch(widgets, x,
(a, b) => a.foo.CompareTo(b.foo));
}
}
虽然排序工作正常,二进制搜索给出一个编译错误无法转换lambda表达式键入“System.Collections.IComparer <的Widget >”,因为它不是一个委托类型。出于某种原因,Sort对IComparer和Comparison都有重载,但BinarySearch只支持IComparer。经过一番研究,我发现了笨重ComparisonComparer<T>
到比较转换为的IComparer:
public class ComparisonComparer<T> : IComparer<T>
{
private readonly Comparison<T> comparison;
public ComparisonComparer(Comparison<T> comparison)
{
this.comparison = comparison;
}
int IComparer<T>.Compare(T x, T y)
{
return comparison(x, y);
}
}
这允许二进制搜索的工作方式如下:
int index = Array.BinarySearch(
widgets,
x,
new ComparisonComparer<Widget>((a, b) => a.foo.CompareTo(b.foo)));
呸。有更清洁的方法吗?
好吧,一种选择是创建类似ProjectionComparer
的东西。我有一个MiscUtil的版本 - 它基本上从投影中创建了一个IComparer<T>
。
所以,你的例子是:
int index = Array.BinarySearch(widgets, x,
ProjectionComparer<Widget>.Create(x => x.foo));
或者你可以实现在T[]
自己的扩展方法做同样的事情:
public static int BinarySearchBy<TSource, TKey>(
this TSource[] array,
TSource value,
Func<TSource, TKey> keySelector)
{
return Array.BinarySearch(array, value,
ProjectionComparer.Create(array, keySelector));
}
备案,ProjectionComparer
你可以用我ValueComparer<T>
class:
int index = Array.BinarySearch(
widgets, x,
new ValueComparer<Widget>(x => x.Foo)
);
您可以通过多个属性进行比较多个lambda表达式。
试试这个:
public static class ComparisonEx
{
public static IComparer<T> AsComparer<T>(this Comparison<T> @this)
{
if (@this == null)
throw new System.ArgumentNullException("Comparison<T> @this");
return new ComparisonComparer<T>(@this);
}
public static IComparer<T> AsComparer<T>(this Func<T, T, int> @this)
{
if (@this == null)
throw new System.ArgumentNullException("Func<T, T, int> @this");
return new ComparisonComparer<T>((x, y) => @this(x, y));
}
private class ComparisonComparer<T> : IComparer<T>
{
public ComparisonComparer(Comparison<T> comparison)
{
if (comparison == null)
throw new System.ArgumentNullException("comparison");
this.Comparison = comparison;
}
public int Compare(T x, T y)
{
return this.Comparison(x, y);
}
public Comparison<T> Comparison { get; private set; }
}
}
它可让您使用此代码:
Comparison<int> c = (x, y) => x == y ? 0 : (x <= y ? -1 : 1);
IComparer<int> icc = c.AsComparer();
Func<int, int, int> f = (x, y) => x == y ? 0 : (x <= y ? -1 : 1);
IComparer<int> icf = f.AsComparer();
ArgumentNullException带有参数名称,没有类型。 – SLaks 2011-03-14 20:26:10
即将到来的.NET4.5有一个方法`的Comparer Create`构建一个`的IComparer 。来自`IComparison `委托的实例。 – 2012-08-08 16:44:42