TakeWhile, but get the element that stopped it also

问题

I'd like to use the LINQ TakeWhile function on LINQ to Objects. However, I also need to know the first element that "broke" the function, i.e. the first element where the condition was not true.

Is there a single function to get all of the objects that don't match, plus the first that does?

For example, given the set {1, 2, 3, 4, 5, 6, 7, 8},

mySet.MagicTakeWhile(x => x != 5);

=> {1, 2, 3, 4, 5}

回答1:

I think you can use SkipWhile, and then take the first element.

var elementThatBrokeIt = data.SkipWhile(x => x.SomeThing).Take(1);

UPDATE

If you want a single extension method, you can use the following:

public static IEnumerable<T> MagicTakeWhile<T>(this IEnumerable<T> data, Func<T, bool> predicate) {
    foreach (var item in data) {
        yield return item;
        if (!predicate(item))
            break;
    }
}

回答2:

LINQ to Objects doesn't have such an operator. But it's straightforward to implement a TakeUntil extension yourself. Here's one such implementation from moreLinq.

回答3:

Just for fun:

var a = new[] 
    {
        "two",
        "three",
        "four",
        "five",
    };
  Func<string, bool> predicate = item => item.StartsWith("t");      
  a.TakeWhile(predicate).Concat(new[] { a.SkipWhile(predicate).FirstOrDefault() })

来源：https://stackoverflow.com/questions/11883469/takewhile-but-get-the-element-that-stopped-it-also