i don’t want to disappoint you but there is no safe way in mxs (and sdk) to get vertex selection (or poly loop/ring) order.
depending on what you want to do it can be a workaround. let’s say if you want to copy some vertex data from one set of verts to another (weights, uvs, etc.) they can be sorted in a specific order…
the idea is to find the right sorting method for the desirable mapping

When I say “in order” I meant in terms of how they are arranged contiguously on the model, as shown in this post:

http://forums.cgsociety.org/showthread.php?f=98&t=639599

(or in this one: http://forums.cgsociety.org/showthread.php?f=98&t=481192 )

I just need something that will do this for multiple groups of selected edges/vertices, creating a separate array for each group…

Maybe this could help:

(
	fn getContinuousEdgeGroups obj =
	(
		local edgesMask = polyop.getEdgeSelection obj
		local selectedEdges = edgesMask as array
		local continuousEdgeGroups = #()
		
		for i in selectedEdges where edgesMask[i] do 
		(
			local newGroup = #{}
			local frontier = #(i)
			
			while frontier.count > 0 do 
			(
				local current = frontier[1]
				deleteItem frontier 1
				edgesMask[current] = off
				newGroup[current] = on
				
				local verts = polyop.getVertsUsingEdge obj current
				local neighbors = polyop.getEdgesUsingVert obj verts
				neighbors *= edgesMask
				neighbors = neighbors as array
				for j in neighbors do
					appendIfUnique frontier j
			)
			
			append continuousEdgeGroups newGroup
		)
		
		continuousEdgeGroups
	)
	
	fn getOrderedEdgeGroups obj continuousEdgeGroups =
	(
		local orderedEdgeGroups = #()
		for edgeGroupMas in continuousEdgeGroups do
		(
			local ends = #()
			local edgeGroup = edgeGroupMas as array
			for i in edgeGroup as array do (
				local verts = polyop.getVertsUsingEdge obj i
				local neighbors = polyop.getEdgesUsingVert obj verts
				neighbors[i] = off
				neighbors *= edgeGroupMas
				if neighbors.numberSet < 2 then
					append ends i
			)
			
			local root
			if ends.count > 0 then (
				-- there is a starting point
				sort ends
				root = ends[1]
			) else (
				-- there is no starting point => this is a loop
				sort edgeGroup
				root = edgeGroup[1]
			)
			
			local newGroup = #()
			local frontier = #(root)
			local usedEdges = #{}
			
			while frontier.count > 0 do (
				local current = frontier[1]
				deleteItem frontier 1
				append newGroup current
				usedEdges[current] = on
				
				local verts = polyop.getVertsUsingEdge obj current
				local neighbors = polyop.getEdgesUsingVert obj verts
				neighbors *= edgeGroupMas
				neighbors -= usedEdges
				neighbors = neighbors as array
				sort neighbors
				join frontier neighbors
			)
			
			append orderedEdgeGroups newGroup
		)
		
		orderedEdgeGroups
	)
	
	if selection.count == 1 and classof $ == Editable_Poly then (
		local obj = $
		local continuousEdgeGroups = getContinuousEdgeGroups obj
		getOrderedEdgeGroups obj continuousEdgeGroups
	)
)

It works about as well as anything I’ve come up with and is also a lot shorter. However, when dealing with closed loops it no longer keeps the edges in order (and also collects the last edge in sequence twice). E.g., what should be #(1,2,3,4) comes up as #(1, 2, 4, 3, 3).

Malkalypse you are right, I didn’t test my code on loops but I did have a special case for it that I should have tested. Here is a fixed version with an extra visualisation / debugging function:

(
	fn getEdgeNeighbors obj i edgesMask:#{} =
	(
		local verts = polyop.getVertsUsingEdge obj i
		local neighbors = polyop.getEdgesUsingVert obj verts
		neighbors[i] = off
		neighbors * edgesMask
	)
	
	fn getContinuousEdgeGroups obj =
	(
		local edgesMask = polyop.getEdgeSelection obj
		local selectedEdges = edgesMask as array
		local continuousEdgeGroups = #()
		
		for i in selectedEdges where edgesMask[i] do 
		(
			local newGroup = #{}
			local frontier = #(i)
			
			while frontier.count > 0 do 
			(
				local current = frontier[1]
				deleteItem frontier 1
				edgesMask[current] = off
				newGroup[current] = on
				
				local neighbors = (getEdgeNeighbors obj current edgesMask:edgesMask) as array
				for j in neighbors do
					appendIfUnique frontier j
			)
			
			append continuousEdgeGroups newGroup
		)
		
		continuousEdgeGroups
	)
	
	fn getOrderedEdgeGroups obj continuousEdgeGroups =
	(
		local orderedEdgeGroups = #()
		for edgeGroupMas in continuousEdgeGroups do
		(
			local ends = #()
			local edgeGroup = edgeGroupMas as array
			for i in edgeGroup as array do (
				local neighbors = getEdgeNeighbors obj i edgesMask:edgeGroupMas
				if neighbors.numberSet < 2 then
					append ends i
			)
			
			local root
			local extraEdge
			if ends.count > 0 then (
				-- there is a starting point
				sort ends
				root = ends[1]
			) else (
				-- there is no starting point => this is a loop
				sort edgeGroup
				root = edgeGroup[1]
				local neighbors = (getEdgeNeighbors obj root edgesMask:edgeGroupMas) as array
				extraEdge = neighbors[1]
				edgeGroupMas[extraEdge] = off
			)
			
			local newGroup = #()
			local frontier = #(root)
			local usedEdges = #{}
			
			while frontier.count > 0 do (
				local current = frontier[1]
				deleteItem frontier 1
				append newGroup current
				usedEdges[current] = on
				
				local neighbors = getEdgeNeighbors obj current edgesMask:edgeGroupMas
				neighbors -= usedEdges
				neighbors = neighbors as array
				sort neighbors
				join frontier neighbors
			)
			
			if extraEdge != undefined then
				append newGroup extraEdge
			
			append orderedEdgeGroups newGroup
		)
		
		orderedEdgeGroups
	)
	
	fn visualizeGroup obj edgeGroup radius:0.1 =
	(
		for i = 1 to edgeGroup.count do (
			local verts = (polyop.getVertsUsingEdge obj edgeGroup[i]) as array
			local faces = (polyop.getFacesUsingEdge obj edgeGroup[i]) as array
			local v1 = polyop.getVert obj verts[1]
			local v2 = polyop.getVert obj verts[2]
			local x = normalize (v2 - v1)
			local y = [0,0,0]
			for j in faces do
				y += polyop.getFaceNormal obj j
			local z = normalize (cross x y)
			y = normalize (cross z x)
			local m = matrix3 x y z ((v1 + v2) / 2)
			local c = cylinder radius:radius wirecolor:red height:(distance v1 v2) pos:v1 dir:x
			Text text:(i as string) wirecolor:red size:(100. * radius) transform:m
		)
	)
	
	local debugMode = true
	if selection.count == 1 and classof $ == Editable_Poly then (
		local obj = $
		local continuousEdgeGroups = getContinuousEdgeGroups obj
		local orderedEdgeGroups = getOrderedEdgeGroups obj continuousEdgeGroups
		if debugMode == true then
			for g in orderedEdgeGroups do
				visualizeGroup obj g
	)
)

There are still unhanded cases, like if you have multiple loops in a single group, for these complex cases I think it’s better to build a directed graph and brake it to form a tree data structure and sort the edges this way, if I’ll have some more spare time tomorrow I can give it a go if you’re interested…

Sure, if you don’t mind! One can never have too many tools, after all

EDIT:
Forgot to mention – that debugging option is really trippy looking!

if we are talking about poly edge loops, it’s much easier to use <EditablePoly>.setLoopShift

edtable poly has already sorted loop structures. so all that you need is

pick any edge from a loop

shift any direction until meet any not from loop or meet the start pick (closed loop)

if you didn’t meet a start pick do shift another direction

merge two sides and get sorted loop edges

Here is the (probably no completely) correct method:

(
	fn getEdgeNeighbors obj i edgesMask:#{} vertMask:#{} =
	(
		local verts = polyop.getVertsUsingEdge obj i
		verts -= vertMask
		local neighbors = polyop.getEdgesUsingVert obj verts
		neighbors[i] = off
		neighbors * edgesMask
	)
	
	struct s_TreeNode
	(
		index,
		Children = #(),
		
		fn getChildren obj &edgesMask:#{} &vertsMask:#{} =
		(
			edgesMask[index] = off
			local neighbors = getEdgeNeighbors obj index edgesMask:edgesMask vertMask:vertsMask
			local NeighborTreeNodes = for i in neighbors collect s_TreeNode index:i
			
			for i in polyop.getVertsUsingEdge obj index do
				vertsMask[i] = on
			
			for i in neighbors where edgesMask[i] do
			(
				local Child = s_TreeNode index:i
				Child.getChildren obj edgesMask:&edgesMask vertsMask:&vertsMask
				append Children Child
			)
		),
		
		fn getGroup =
		(
			local edgeGroup = #(index)
			for Child in Children do
				join edgeGroup (Child.getGroup())
			edgeGroup
		)
	)
	
	fn getContinuousEdgeGroups obj =
	(
		local edgesMask = polyop.getEdgeSelection obj
		local selectedEdges = edgesMask as array
		local continuousEdgeGroups = #()
		
		for i in selectedEdges where edgesMask[i] do 
		(
			local newGroup = #{}
			local frontier = #(i)
			
			while frontier.count > 0 do 
			(
				local current = frontier[1]
				deleteItem frontier 1
				edgesMask[current] = off
				newGroup[current] = on
				
				local neighbors = (getEdgeNeighbors obj current edgesMask:edgesMask) as array
				for j in neighbors do
					appendIfUnique frontier j
			)
			
			append continuousEdgeGroups newGroup
		)
		
		continuousEdgeGroups
	)
	
	fn getOrderedEdgeGroups obj continuousEdgeGroups =
	(
		local orderedEdgeGroups = #()
		for edgeGroupMas in continuousEdgeGroups do
		(
			local ends = #()
			local edgeGroup = edgeGroupMas as array
			for i in edgeGroup do 
			(
				local isEndEdge = false
				local verts = polyop.getVertsUsingEdge obj i
				for j in verts do
				(
					local neighbors = polyop.getEdgesUsingVert obj j
					neighbors *= edgeGroupMas
					if neighbors.numberSet == 1 then
						exit with isEndEdge = true
				)
				
				if isEndEdge then
					append ends i
			)
			
			local Root = s_TreeNode index:(if ends.count > 0 then ends[1] else edgeGroup[1])
			Root.getChildren obj edgesMask:edgeGroupMas
			append orderedEdgeGroups (Root.getGroup())
		)
		
		orderedEdgeGroups
	)
	
	fn visualizeGroup obj edgeGroup radius:0.1 =
	(
		for i = 1 to edgeGroup.count do 
		(
			local verts = (polyop.getVertsUsingEdge obj edgeGroup[i]) as array
			local faces = (polyop.getFacesUsingEdge obj edgeGroup[i]) as array
			local v1 = polyop.getVert obj verts[1]
			local v2 = polyop.getVert obj verts[2]
			local x = normalize (v2 - v1)
			local y = [0,0,0]
			for j in faces do
				y += polyop.getFaceNormal obj j
			local z = normalize (cross x y)
			y = normalize (cross z x)
			local m = matrix3 x y z ((v1 + v2) / 2)
			local c = cylinder radius:radius wirecolor:red height:(distance v1 v2) pos:v1 dir:x
			Text text:(i as string) wirecolor:red size:((distance v1 v2) / 2) transform:m
		)
	)
	
	local debugMode = true
	if selection.count == 1 and classof $ == Editable_Poly then 
	(
		local obj = $
		local continuousEdgeGroups = getContinuousEdgeGroups obj
		local orderedEdgeGroups = getOrderedEdgeGroups obj continuousEdgeGroups
		if debugMode == true then
			for g in orderedEdgeGroups do
				visualizeGroup obj g
	)
)

If the debugging option doesn’t work very well it’s probably because it’s scale dependent, I didn’t bother making it scale independent :shrug:

EDIT: Already fixed a few issues

After some poking and prodding, I think I get how it works now. One question though, what would need changing in order to collect the vertices in order instead of the edges?