Using linq to retrieve pairs of Points from collection?

Question

I have a collection of Points, stored in a PointCollection.

I need the points in the collection to draw lines.

So, for example, if a point collection has four points, that will be three lines.

Example:

(1) Point(1,1) (2) Point(2,2) (3) Point(3,3) (4) Point(4,4)

If I have a list of points, comprised of the four points referenced above, I am going to draw three lines, using the following logic:

Line 1 - Point(1,1), Point(2,2) Line 2 - Point(2,2), Point(3,3) Line 3 - Point(3,3), Point(4,4)

Is there a way, using Linq, Lambda Expressions, Extension Methods etc., to extract these points in pairs, from my initial list of points? That way I can iteratively take each pair of points and draw my lines?

Thanks.

Answer 1

I'm off out in a second, but here's a horrible solution (in that it uses side-effects):

Point previous = default(Point);

return points.Select(p => { Point tmp = previous;
                            previous = p;
                            return new { p1 = tmp, p2 = previous };
                          })
             .Skip(1); // Ignore first (invalid) result

You can probably do better with System.Interactive and Scan, but otherwise it would probably be best to write a new extension method. Something like this (using Tuple from C# 4):

public static IEnumerable<Tuple<T, T>> ConsecutivePairs<T>(this IEnumerable<T> sequence)
{
    // Omitted nullity checking; would need an extra method to cope with
    // iterator block deferred execution
    using (IEnumerator<T> iterator = sequence.GetEnumerator())
    {
        if (!iterator.MoveNext())
        {
            yield break;
        }
        T previous = iterator.Current;
        while (iterator.MoveNext())
        {
            yield return Tuple.Create(previous, iterator.Current);
            previous = iterator.Current;
        }
    }
}

(Apologies for any mistakes - written in a hurry!)