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make specific cluster


I have set of coordinates. I want to make clusters in which every point is within 1.5 distance unit of it's neighbor.


ex of point coordinates:


{{-12.945, 20.6509, 12.5901}, {-13.4452, 20.307, 111.626}, 

{-12.9731, 22.8458, 12.4215}, {-13.2381, 24.8167, 10.7147}, 
{-11.3668, 23.3908,11.8499}, {-11.6828, 23.7311, 10.8839}, 
{-13.3929, 21.1835, 9.86324}, {-11.5016, 21.3324, 10.1392}, 
{-12.3079, 22.096, 8.57246}, {-12.5268, 20.9679, 10.5444}, 
{-12.1951, 24.5423, 10.1807}, {-11.8887, 22.3883, 10.0751}, 
{-14.2529, 20.4808, 9.81084}, {-11.9876, 21.8094, 11.0478}, 
{-12.3718, 23.6176, 11.8266}, {-11.6179, 20.8324, 11.2154}, 
{-12.5927, 21.7492, 12.5087}, {-12.1665, 24.6649, 11.2909}, 
{-12.3854, 21.5571, 9.51876}, {-12.2237, 23.4278, 9.9787}}


what is the quickest way in Mathematica for this (for large data sets).


I tried this to find all points that are within mentioned distance:


Table[Select[List, EuclideanDistance[List[[i]], #] < 1.5 &], {i, 1, Length[[List]]}]

but now I have troubles to join all sets that have common elements.



Answer



Here is a possible alteernative, I was working on while Kuba posted his answer :-) I also started by using FixedPoint and the inner loop seems to work but the outer one is easier with While.


c = {{-12.945, 20.6509, 12.5901}, {-13.4452, 20.307, 
    111.626}, {-12.9731, 22.8458, 12.4215}, {-13.2381, 24.8167, 
    10.7147}, {-11.3668, 23.3908, 11.8499}, {-11.6828, 23.7311, 

    10.8839}, {-13.3929, 21.1835, 9.86324}, {-11.5016, 21.3324, 
    10.1392}, {-12.3079, 22.096, 8.57246}, {-12.5268, 20.9679, 
    10.5444}, {-12.1951, 24.5423, 10.1807}, {-11.8887, 22.3883, 
    10.0751}, {-14.2529, 20.4808, 9.81084}, {-11.9876, 21.8094, 
    11.0478}, {-12.3718, 23.6176, 11.8266}, {-11.6179, 20.8324, 
    11.2154}, {-12.5927, 21.7492, 12.5087}, {-12.1665, 24.6649, 
    11.2909}, {-12.3854, 21.5571, 9.51876}, {-12.2237, 23.4278, 
    9.9787}};
MyClustering[data_List, distance_?NumericQ] :=
 Module[{dataoriginal = data, res = {}, temp = {}},

  While[dataoriginal =!= {},
   temp = {};
   AppendTo[res,
    FixedPoint[(
       Map[
        Function[p, 
         temp = Join[temp, 
           Select[dataoriginal, EuclideanDistance[#, p] < distance &]];
         dataoriginal = Complement[dataoriginal, temp]], #]; 
       temp) &, {dataoriginal[[1]]}]]];

  Return[res]]

Just few notes: dataoriginal is needed because I modify the original list and the argument of a function (data in that case) cannot be modified inside the function's body. For huge lists AppendTo is generally slow, so a possible alternative is


res = Join[{res}, FixedPoint[...]]


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