knn.pi

% translated from https://gist.github.com/jpjacobs/6190830a08b95b0bd984
import util.

% csv parsing code placeholder
% Arr={A:L in 1..length(Lines), Z=Lines[L], A={N: C in Z.split(","), N=parse_term(C)}}

matrix_square_sub_total(M) = M3 =>
    M3 = new_array(M.length, M.length),
    foreach(I in 1..M.length, J in 1..M.length)
        M3[I,J] = sum([pow(M[I,K]-M[J,K],2) : K in 1..M[1].length])
    end.

grade_up(L) = [ I : (E,I) in sort([(E,I) : {E,I} in zip(L,1..L.length)])].

knn(K,M) = Ret =>    
    M2 = matrix_square_sub_total(M),
    % writeln(M2),
    Ret = new_array(M2.length, M2[1].length),
    foreach(I in 1..M2.length)
        Count:=1,
        Sort = tail(grade_up(rows(M2[I]))),
        foreach(J in 1..M2[1].length)
            % sort by the difference from the current value
            if I==J then % skip self
                Val = ''
            elseif J==Sort[Count] && Count <= K  then
                Val = M2[I,J],
                Count := Count + 1
            else
                Val = ''
            end,    
            Ret[I,J] = Val
       end
    end,
    % make symmetric
    T=transpose(Ret),
    foreach(I in 1..M2.length, J in 1..M2[1].length)
        if Ret[I,J] == '' && T[I,J] != '' then
            Ret[I,J] := T[I,J]
        end
    end,
    true.

main=>
    M = {{0,1,2,3,4},{5,6,7,8,9},{10,11,12,13,14},{15,16,17,18,19},{20,21,22,23,24}},
    Arr = knn(1,M),
    writeln(Arr),
    true.

/*

Picat> L=knn(1,{{0,1,2},{3,4,5},{6,7,8}})
L = {{'',27,''},{27,'',27},{'',27,''}}


1 knn i. 3 3
 _ 27 _
27  _ _
 _ 27 _


Picat> L=knn(2,{{0,1,2},{3,4,5},{6,7,8}})
L = {{'',27,108},{27,'',27},{108,27,''}}

2 knn i. 3 3
  _ 27 108
 27  _  27
108 27   _


Picat> L=knn(1,{{0,1,2,3},{4,5,6,7},{8,9,10,11},{12,13,14,15}})
L = {{'',64,'',''},{64,'',64,''},{'',64,'',64},{'','',64,''}}

1 knn i. 4 4
 _ 64  _  _
64  _ 64  _
 _ 64  _ 64
 _  _ 64  _



Picat> L=knn(2,{{0,1,2},{3,4,5},{6,7,8},{9,10,11,12}})
L = {{'',27,108,''},{27,'',27,''},{108,27,'',27},{'','',27,''}}

 2 knn i. 4 3
  _  27 108   _
 27   _  27 108
108  27   _  27
  _ 108  27   _
   
*/