Prune points but keep list order

Hello everyone,

I’m trying to prune duplicate points (same x,y but diff z) and keep the point with the lower z-value.
For example, I want to make this table:


And end up with this:
image

Grouping by their X values and sub grouped by their Y values, then subgroups are sorted by their Z values doesnt work entirely work because it won’t keep list order. ie this way Points above each other - #2 by Vikram_Subbaiah
Ended up with this:
image

However, this way works exactly how I wanted - Create Toposurface from Floor - #5 by Nick_Boyts
But as predicted by Nick_Boyts, the cross lacing takes too long for large lists.

Is there another OOTB way to get what I want for big lists? Is there a python script around that find the duplicates?

  1. Pull the point’s X and Y values, and merge them into a string. (p.X+””+p.Y;)

  2. Group the points by that string using a List.GroupByKey.

  3. List.MinimumItemByKey with correct lacing and list level input, using a Point.Z node as the projector will pull the lowest Z from each group.

No cross product lacing involved - the grouping will likely be the slowest action. Fortunately you could quickly limit that to quadrants of your project by only selecting points in one area at a time.

Keeping track of the corresponding indices as you group, sort and filter the points would allow you to rearrange the points

prune.dyn (28.0 KB)

3 Likes

Hello
an alternative with Python

import sys
import clr
clr.AddReference('ProtoGeometry')
from Autodesk.DesignScript.Geometry import *

def XYHasAlready(pt):
	global pruneLst
	for idx, i in enumerate(pruneLst):
		if abs(i.X - pt.X) < 0.01 and abs(i.Y - pt.Y) < 0.01:
			if pt.Z < i.Z:
				pruneLst[idx] = pt
			return True
	return False
	
inputPts = IN[0]
pruneLst = []

for pt in inputPts:
	if not XYHasAlready(pt):
		pruneLst.append(pt)
		
OUT = pruneLst
3 Likes

Thanks everyone. I tried all three with success.