从C#中的列表中选择唯一元素

Question

如何从列表中选择唯一元素{0, 1, 2, 2, 2, 3, 4, 4, 5}以便{0, 1, 3, 5}有效地删除重复元素的所有实例{2, 4}？

Answer 1

var numbers = new[] { 0, 1, 2, 2, 2, 3, 4, 4, 5 };

var uniqueNumbers =
    from n in numbers
    group n by n into nGroup
    where nGroup.Count() == 1
    select nGroup.Key;

// { 0, 1, 3, 5 }

Answer 2

var nums = new int{ 0...4,4,5};
var distinct = nums.Distinct();

确保你使用的是Linq和.NET framework 3.5.

Answer 3

随着lambda ..

var all = new[] {0,1,1,2,3,4,4,4,5,6,7,8,8}.ToList();
var unique = all.GroupBy(i => i).Where(i => i.Count() == 1).Select(i=>i.Key);

Answer 4

C#2.0解决方案:

static IEnumerable<T> GetUniques<T>(IEnumerable<T> things)
{
    Dictionary<T, int> counts = new Dictionary<T, int>();

    foreach (T item in things)
    {
        int count;
        if (counts.TryGetValue(item, out count))
            counts[item] = ++count;
        else
            counts.Add(item, 1);
    }

    foreach (KeyValuePair<T, int> kvp in counts)
    {
        if (kvp.Value == 1)
            yield return kvp.Key;
    }
}

Answer 5

如果列表中有复杂的类型对象并希望获取属性的唯一值,则这是另一种方法:

var uniqueValues= myItems.Select(k => k.MyProperty)
                  .GroupBy(g => g)
                  .Where(c => c.Count() == 1)
                  .Select(k => k.Key)
                  .ToList();

或者获得不同的值:

var distinctValues = myItems.Select(p => p.MyProperty)
                            .Distinct()
                            .ToList();

如果您的属性也是复杂类型,则可以为Distinct()创建自定义比较器,例如Distinct(OrderComparer),其中OrderComparer可能如下所示:

public class OrderComparer : IEqualityComparer<Order>
{
    public bool Equals(Order o1, Order o2)
    {
        return o1.OrderID == o2.OrderID;
    }

    public int GetHashCode(Order obj)
    {
        return obj.OrderID.GetHashCode();
    }
}