Array of unique points?

thomthom

When you have an array of arbitrary points - and you want to ensure that array only contains unique points, how do you filter them out?

points.uniq! doesn't seem to work.

Example:

` point1 = Geom::Point3d.new 1,1,1

Point3d(1, 1, 1)
point2 = Geom::Point3d.new 10,10,10
Point3d(10, 10, 10)
point3 = Geom::Point3d.new 10,10,10
Point3d(10, 10, 10)
a = [point1, point2, point3]
[Point3d(1, 1, 1), Point3d(10, 10, 10), Point3d(10, 10, 10)]
a.uniq
[Point3d(1, 1, 1), Point3d(10, 10, 10), Point3d(10, 10, 10)]`

Chris Fullmer

Any chance you are getting the points from an array of vertices? Vertices will respond to the uniq(!) methods. I can't think of any time that I actually sorted by Point3d objects. And I tihnk it was because I found it easier to use vertices, which has always worked out ok for what I was writing.

Chris

thomthom

No, not vertices. computed intersections.

thomthom

atm I got this code:


def self.uniq_points(points)
  old_points = points.clone
  new_points = []
  until old_points.empty?
    point = old_points.shift
    point_exists = false
    new_points.each { |p|
      if p == point
        point_exists = true
        break
      end
    }
    new_points << point unless point_exists
  end
  return new_points
end

but I was wondering if there was a better method....

Chris Fullmer

Yeah, as I was thinking - each Point3d object is its own object, and therefore different, even though they might share the same coordinates in space.

You need to compare them as strings I suppose, since I see no quicker comparison method(?). Try this line:

` a = [point1.inspect, point2.inspect, point3.inspect]

a.uniq`

That should work, I don't know how slow it will be if its over zillions of points though,

Chris

thomthom

no, not string. you can compare two points - point1 == point2 if return true if they are the same point, withing some tolerance SU has set. But it seems that array.uniq doesn't do this type of comparison...

TIG

Point3d's will be uniq!'d if they have the same ID BUT NOT if they have just the same XYZ values [they aren't really equal are they?], but we can write a simple def to sort it out...


def unique(pointsIN = [])
  return pointsIN if pointsIN.to_a[0].class != Geom;;Point3d
  # we'll only process an array of Point3d's ?
  points_a = []; pointsIN.to_a.compact.each{|p| points_a << p.to_a}; pointsa.uniq!
  # we compact to remove any 'nil' entries ?
  pointsOUT = []; points_a.each{|p| pointsOUT << Geom.Point3d.new(p.x, p.y, p.z)}
  return pointsOUT
end#def
# Assuming a list [array] of Point3d's that might contain duplicates called 'points' then...
points = unique points
# will give us a list [array] of unique Point3d's called 'points'...

TIG

Alternatively, following TT's point1 == point2 idea


def unique(pointsIN = [])
  pointsOUT=[]
  pointsIN.to_a.each{|p|
    duplicated = false
    pointsOUT.each{|po|
      if po == p
        duplicated = true
        break
      end#if
    }
    pointsOUT << p if not duplicated
  }
  return pointsOUT
end#def
points = points unique

Which keeps the Point3d's IDs unchanged...

MartinRinehart

@thomthom said:

But it seems that array.uniq doesn't do this type of comparison...

Have you tried just adding them to a set?

thomthom

I was pretty sure I'd tried that! But clearly I haven't!

` point1 = Geom::Point3d.new 1,1,1

Point3d(1, 1, 1)
point2 = Geom::Point3d.new 10,10,10
Point3d(10, 10, 10)
point3 = Geom::Point3d.new 10,10,10
Point3d(10, 10, 10)
s = Set.new
#Set:0xbd7da68
s.insert(point1)
#Set:0xbd7da68
s.insert(point2)
#Set:0xbd7da68
s.insert(point3)
#Set:0xbd7da68
s.to_a
[Point3d(1, 1, 1), Point3d(10, 10, 10)]`

Very interesting that it evaluates differently. It compares the values, not the objects.
Exactly the kind of solution I was hoping for.