Question

我知道有两种方法可以从支持显式比较的对象数组中删除双打：

使用HashSet构造函数和
使用LINQ的Distinct（）。

如何从结构数组中删除双精度数，仅将数组成员与单个字段进行比较？换句话说，如何编写可以由Distinct（）使用的谓词。

此致

Answer 1

好吧，你可以实现IEqualityComparer<T>来挑选该字段并将其用于相等测试和散列...或者你可以使用DistinctBy MoreLINQ 3}}

当然，您不必非常依赖MoreLINQ - 您可以非常简单地实现它：

public static IEnumerable<TSource> DistinctBy<TSource, TKey>
    (this IEnumerable<TSource> source,
     Func<TSource, TKey> keySelector)
{
    // TODO: Implement null argument checking :)

    HashSet<TKey> keys = new HashSet<TKey>();
    foreach (TSource element in source)
    {
        if (knownKeys.Add(keySelector(element)))
        {
            yield return element;
        }
    }
}

Answer 2

我可能只是循环：

var values = new HashSet<FieldType>();
var newList = new List<ItemType>();
foreach(var item in oldList) {
    if(hash.Add(item.TheField)) newList.Add(item);
}

Answer 3

之前发布过LINQ答案。我正在复制Richard Szalay的回答：Filtering duplicates out of an IEnumerable

public static class EnumerationExtensions
{
    public static IEnumerable<TSource> Distinct<TSource,TKey>(
        this IEnumerable<TSource> source, Func<TSource,TKey> keySelector)
    {
        KeyComparer comparer = new KeyComparer(keySelector);

        return source.Distinct(comparer);
    }

    private class KeyComparer<TSource,TKey> : IEqualityComparer<TSource>
    {
        private Func<TSource,TKey> keySelector;

        public DelegatedComparer(Func<TSource,TKey> keySelector)
        {
            this.keySelector = keySelector;
        }

        bool IEqualityComparer.Equals(TSource a, TSource b)
        {
            if (a == null && b == null) return true;
            if (a == null || b == null) return false;

            return keySelector(a) == keySelector(b);
        }

        int IEqualityComparer.GetHashCode(TSource obj)
        {
            return keySelector(obj).GetHashCode();
        }
    }
}

正如理查德所说的那样，就像这样使用：

var distinct = arr.Distinct(x => x.Name);

Answer 4

实施自定义IEqualityComparer<T>

public class MyStructComparer : IEqualityComparer<MyStruct>
{
    public bool Equals(MyStruct x, MyStruct y)
    {
        return x.MyVal.Equals(y.MyVal);
    }

    public int GetHashCode(MyStruct obj)
    {
        return obj.MyVal.GetHashCode();
    }
}

然后

var distincts = myStructList.Distinct(new MyStructComparer());

从结构数组中删除双精度数

4 个答案: