c# - Alternatives to nested Select in Linq -

working on clustering project, stumbled upon this, , i'm trying figure out if there's better solution 1 i've come with.

problem : given list<point> points of points in r^n ( can think @ every point double array fo dimension n), double mindistance , distance func<point,point,double> dist , write linq expression returns, each point, set of other points in list closer him mindistance according dist.

my solution following:

        var lst = points.select(                  x => points.where(z => dist(x, z) < mindistance)                     .tolist() )                 .tolist(); 

so, after noticing that

• using linq not best idea, because calculate every distance twice
• the problem doesn't have practical use
• my code, if bad looking, works

i have following questions:

1. is possible translate code in query expression? , if so, how?
2. is there better way solve in dot notation?

the problem definition, want "for each point, set of other points" makes impossible solve without inner query - disguise in clever manner. if change data storage policy, , don't stick linq then, in general, there many approaches nearest neighbour search problem. example hold points sorted according values on 1 axis, can speed-up queries neighbours eliminating candidates without full distance calculation. here paper approach: flexible metric nearest neighbor classification.