Topic: Finding the min point in a collection of points

[Proctor]

Hello: I was wondering if there was any method available using autocad .net api to find the min point in
a collection of points?

Thank you,
Proctor

Note: Using Autocad 2009

[It's Alive!]

maybe something like.?.

Code: [Select]

           
            _AcDb.Extents3d extents = new _AcDb.Extents3d();
            foreach (_AcGe.Point3d point in _AcGe.Point3dCollection)
               extents.AddPoint(point);
            extents.MinPoint;


[Kerry]

maybe something like.?.

Code: [Select]

           
            _AcDb.Extents3d extents = new _AcDb.Extents3d();
            foreach (_AcGe.Point3d point in _AcGe.Point3dCollection)
               extents.AddPoint(point);
            extents.MinPoint;


That sure beats converting the Collection to a List and running a Linq .Orderby on the list

[gile]

Hi

What does "min point" mean ?

In a collection containing 2 point : { (1, 0),  (0, 1) }, which is the "min point" ?
For this collection, Daniel's method should return (0, 0) as "min point" which does not belong to the collection.

I think you have to define more precisely the criteria used for "min point" and this criteria can be use with the IEnumerable .OrderBy() Linq extension method as Kerry said or the List<T>.Sort().

But as you don't have to sort the whole collection, the Linq Aggregate() extension method should be faster.

Example to get the "min point" comparing X coordinate first, then Y in case of equality, then Z.

Code: [Select]

        private Point3d MinPoint(IEnumerable<Point3d> pts)
        {
            return pts.Aggregate((p1, p2) =>
                {
                    if (p1.X == p2.X)
                    {
                        if (p1.Y == p2.Y)
                        {
                            if (p1.Z < p2.Z) return p1;
                            else return p2;
                        }
                        else if (p1.Y < p2.Y) return p1;
                        else return p2;
                    }
                    else if (p1.X < p2.X) return p1;
                    else return p2;
                });
        }
If you're not comfortable with lambda expressions, you can define a separated method for the accumulator

Exemple comaparing the coordinates sum first, then X then Y coordinate

Code: [Select]

        private Point3d ComparePoints(Point3d p1, Point3d p2)
        {
            double s1 = p1.X + p1.Y + p1.Z;
            double s2 = p2.X + p2.Y + p2.Z;
            if (s1 == s2)
            {
                if (p1.X == p2.X)
                {
                    if (p1.Y < p2.Y) return p1;
                    else return p2;
                }
                else if (p1.X < p2.X) return p1;
                else return p2;
            }
            else if (s1 < s2) return p1;
            else return p2;
        }
        ...
        Point3d minPt = pts.Aggregate(ComparePoints)


[Proctor]

Thank you all for your replies. To better define what I mean when I want to find the min point....
I would like to find the point in the collection that has the minx and miny.

gile, do you think using private Point3d ComparePoints(Point3d p1, Point3d p2)
would work for this situation?

Thanks again,
Proctor

[gile]

gile, do you think using private Point3d ComparePoints(Point3d p1, Point3d p2)
would work for this situation?

I cannot reply for you.
In most cases, yes. The coordinates sum will do the trick.
But you have to think about the cases this sum is equal for two or more points: (0, 1, 0) (1, 0, 0) (3, -2, 0) (-1, 2, 0)... which of these do you consider "the min point" ?
Actually, the ComparePoints method returns the lowest X coordinate (-1, 2, 0).

[LE3]

here we use a lot linq...

so something like:

IEnumerable<Point3d> query = pts.Cast<Point3d>();
double x = query.Min(p => p.X);
Point3d pt = query.First(p => p.X == x);

To get the point with the min() X... and start exploring from there (tons of samples around the net about linq) - hth