检查所有列表项是否在C＃中具有相同的成员值

Question

I'm searching for a simple and fast way to check if all my Listitems have the same value for a member.

foreach (Item item in MyList)
{
    Item.MyMember = <like all other>;
}

EDIT: I forgot one thing: If one of this members (its a string) is String.Empty and all other items have the same string it should be true too! Sorry i forgot this.

Answer 1

EDIT: Okay, after the new requirement has

bool allSame = !MyList.Select(item => item.MyMember)
                      .Where(x => !string.IsNullOrEmpty(x))
                      .Distinct()
                      .Skip(1)
                      .Any();

That avoids you having to take a first step of finding one sample value to start with. (And it will still exit as soon as it finds the second value, of course.)

It also only iterates over the sequence once, which may be important if it's not really a repeatable sequence. Not a problem if it's a List<T> of course.

EDIT: To allay concerns over Skip , from the documentation:

If source contains fewer than count elements, an empty IEnumerable<T> is returned. If count is less than or equal to zero, all elements of source are yielded.

Answer 2

你自己的解决方案已经足够简单，但是如果你想抽象出循环并更有表现力地写它，你可以使用Linq。

bool allSame = MyList.All(item => item.MyMember == someValue);

Answer 3

using System.Linq;
…

if (myList.Any()) // we need to distinguish between empty and non-empty lists 
{
    var value = myList.First().MyMember;
    return myList.All(item => item.MyMember == value);
}
else
{
    return true;  // or false, if that is more appropriate for an empty list    
}

Answer 4

Here is a generic one that works for all version of .NET beginning with 2.0:

public static bool AllSameByProperty<TItem, TProperty>(IEnumerable<TItem> items, Converter<TItem, TProperty> converter)
{
    TProperty value = default(TProperty);
    bool first = true;

    foreach (TItem item in items)
    {
        if (first)
        {
            value = converter.Invoke(item);
            first = false;
            continue;
        }

        TProperty newValue = converter.Invoke(item); 

        if(value == null)
        {
            if(newValue != null)
            {
                return false;
            } 

            continue;
        }

        if (!value.Equals(newValue))
        {
            return false;
        }
    }

    return true;
}

Its usage in C# 2.0:

AllSameByProperty(list, delegate(MyType t) { return t.MyProperty; });

Its usage in C# 3.0:

AllSameByProperty(list, t => t.MyProperty);

Answer 5

我认为这是最短，最优雅的解决方案：

bool allSame = list.GroupBy(item => item.TheProperty).Count == 1;

Answer 6

Iam doing like so:

Item item = MyList.FirstOrDefault(x=>x.MyMember != valueToMatch);
bool allMembersSame = item == null;