TakeWhile, but get the element that stopped it also

Question

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 elem

Answer 1

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.

Answer 2

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;
    }
}

Answer 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() })