Extension method that will yield properties from a specified group of properties if any of them are encountered in the first collection. It's using the group metaphore because I use it for grouping properties together by name in a UI. Yes there's perf issues as things get big, it's your foot.

OrderGroupAtFirstOccurance.cs

/// <summary>
/// Let's say you have a collection of things with an indeterminate ordering but when you
/// enumerate the things, you'd like a subset to be grouped together. That's what this
/// can do but there's no guarantee elements in the group parameter exist in the primaryCollection.
/// That can be seen as a bug or a feature, it's up to you.
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="primaryCollection"></param>
/// <param name="group"></param>
/// <returns></returns>
public static IEnumerable<T> OrderedGroupAtFirstOccurance<T>(this IEnumerable<T> primaryCollection, IEnumerable<T> group) {
    bool groupEnumerated = false;
    foreach (var i in primaryCollection) {
        if (group.Contains(i)) {
            if (!groupEnumerated) {
                foreach (var t in group) {
                    yield return t;
                }
                groupEnumerated = true;
            }
        } else {
            yield return i;
        }
    }
}