How to get the index of an item in a list in a single step?

Question

How can I find the index of an item in a list without looping through it?

Currently this doesn\'t look very nice - searching through the list for the same item twice

Answer 1

Here's a copy/paste-able extension method for IEnumerable

public static class EnumerableExtensions
{
    /// 

    /// Searches for an element that matches the conditions defined by the specified predicate,
    /// and returns the zero-based index of the first occurrence within the entire .
    /// 
    /// 
    /// The list.
    /// The predicate.
    /// 
    /// The zero-based index of the first occurrence of an element that matches the conditions defined by , if found; otherwise it'll throw.
    /// 
    public static int FindIndex(this IEnumerable list, Func predicate)
    {
        var idx = list.Select((value, index) => new {value, index}).Where(x => predicate(x.value)).Select(x => x.index).First();
        return idx;
    }
}

Enjoy.