sorting and interpolation

I hope that I can get coding ideas (pseudo matlab code) or matlab examples or complete matlab codes for the following problems. 1. For all the points R in 3-dim coordinates (x, y, z), find each sets of contiguous and neighboring points (such as S0, S1 etc.) which has the same R values (such as R0, R1 etc.). I guess sort function can do this job. 2. Find if there are points that can be found by interpolation using nearby points for all the points except the interior points of above sets (S0, S1….) that is, the points which doesn’t have neighboring points with the same R value + only the perimeter points of the above sets. If there are points satisfying the conditions. find the nearby points to be used for the interpolations and the distances from the points. I guess interp3 and finding the small errors between the real R value and the interp3 value can do the job.