Pair Nearest

Pair nearest while avoiding reverse pairing (unique pairs)
s = PolyCurve.ByJoinedCurves(List.Shuffle(
(Rectangle.ByWidthLength(10..20..#5,5).Translate
(0..40..#5,0..40..#5,0))).Explode());
def cns(cr:var[]..[], oc:var[]..[])
{
a = List.SetDifference(List.RestOfItems(cr),oc);
b = cr[0].DistanceTo(a);
c = List.SortByKey(a,b)["sorted list"];
return List.FirstItem(c);
};
s;
nearestPairs = [Imperative]
{
t = [];
i = 0;
while (List.Count(t)<List.Count(s))
{
d = cns(List.ShiftIndices(s,-i),t);
t = List.AddItemToEnd(d,t);
i = i + 1;
}
return List.Transpose([s,t]);
};