How to move elements from one LinkedList to another based on criteria

Question

I have two LinkedLists, I'd like to move all elements which match some criteria from LinkedListA to LinkedListB (LinkedListB is not empty to start with). Any ideas?

Answer 1

If you're moving from list a to the end of list b, try this method:

// .Net 2.0 compatable
private static void moveFromFirstToSecond<T>(Predicate<T> match, LinkedList<T> first, LinkedList<T> second)
{
    LinkedListNode<T> current = first.First;
    while (current != null)
    {
        LinkedListNode<T> next = current.Next;
        if (match(current.Value))
        {
            second.AddLast(current.Value); // second.AddLast(current) also works
            first.Remove(current);
        }
        current = next;
    }
}

// for strings that start with "W"
LinkedList<string> a = ...
LinkedList<string> b = ...
moveFromFirstToSecond(delegate(string toMatch)
    { return toMatch.StartsWith("W"); }, a, b);

or as an extension method:

// .Net 3.5 or later
public static void MoveMatches<T>(this LinkedList<T> first, Predicate<T> match, LinkedList<T> other)
{
    LinkedListNode<T> current = first.First;
    while (current != null)
    {
        LinkedListNode<T> next = current.Next;
        if (match(current.Value))
        {
            other.AddLast(current.Value); // other.AddLast(current) also works
            first.Remove(current);
        }
        current = next;
    }
}

// for strings that start with "W"
LinkedList<string> a = ...
LinkedList<string> b = ...
a.MoveMatches(x => x.StartsWith("W"), b);