我如何从Linq的TakeWhile中再拿一件物品？

Question

(感兴趣的代码行是最后一行,其余的只是完整的代表)

使用下面的代码,我想拿VOTERS直到我超过所需的最大票数,但它在达到最大票数之前就停止了,所以我的选民人数比我想要的少了1个.

在LINQ中是否有一个干净的方式,我可以在它达到最大票数之前获得投票？我知道我可以添加一个选民或者在循环中执行此操作但我很好奇是否有一个很好的方法来使用LINQ.

var voters = new List<Person>
                             {
                                 new Person("Alice", Vote.Yes ),
                                 new Person("Bob", Vote.Yes),
                                 new Person("Catherine", Vote.No),
                                 new Person("Denzel", Vote.Yes),
                                 new Person("Einrich", Vote.Abstain),
                                 new Person("Frederica", Vote.Abstain),
                                 new Person("Goeffried", Vote.Abstain),
                             };
            voters.Single(c => c.Name == "Alice").Voices = 100;
            voters.Single(c => c.Name == "Bob").Voices = 150;
            voters.Single(c => c.Name == "Catherine").Voices = 99;
            voters.Single(c => c.Name == "Denzel").Voices = 24;
            voters.Single(c => c.Name == "Einrich").Voices = 52;
            voters.Single(c => c.Name == "Frederica").Voices = 39;
            voters.Single(c => c.Name == "Goeffried").Voices = 99;

// this takes voters until we are BEFORE reaching X voices...
int voicesSoFar = 0;
int voicesNeeded = 300;
var eligibleVoters = voters.TakeWhile((p => (voicesSoFar += p.Voices) < voicesNeeded ));

Answer 1

在我想要执行一个函数直到并包含它达到最终条件的情况下,我做了:

public static IEnumerable<T> TakeUntilIncluding<T>(this IEnumerable<T> list, Func<T, bool> predicate)
{
    foreach(T el in list)
    {
        yield return el;
        if (predicate(el))
            yield break;
    }
}

为我工作!我认为这是一个与Jason相似的与实现无关的解决方案,但更简单.

Answer 2

您正在寻找

voters.TakeWhile(p => {
   bool exceeded = voicesSoFar > voicesNeeded ;
   voicesSoFar += p.Voices;
   return !exceeded;
});

如果你坚持使用单行,这将通过比较之前的值来实现:

voters.TakeWhile(p => (voicesSoFar += p.Voices) - p.Voices < voicesNeeded);

Answer 3

只需编写自己的扩展方法:

static class IEnumerableExtensions {
    public static IEnumerable<T> TakeUntil<T>(
        this IEnumerable<T> elements,
        Func<T, bool> predicate
    ) {
        return elements.Select((x, i) => new { Item = x, Index = i })
                       .TakeUntil((x, i) => predicate(x.Item))
                       .Select(x => x.Item);
    }

    public static IEnumerable<T> TakeUntil<T>(
        this IEnumerable<T> elements,
        Func<T, int, bool> predicate
    ) {
        int i = 0;
        foreach (T element in elements) {
            if (predicate(element, i)) {
                yield return element;
                yield break;
            }
            yield return element;
            i++;
        }
    }
}

用法:

var eligibleVoters = voters.TakeUntil(
                         p => (voicesSoFar += p.Voices) >= voicesNeeded
                     );

foreach(var voter in eligibleVoters) {
    Console.WriteLine(voter.Name);
}

输出:

Alice
Bob
Catherine