function [B,breakpts] = addcoarsecol (A,C,N)

% ADDCOARSECOL coarsens (bins) a column of a matrix.
%
% B = addcoarsecol (A,C,N)
%
% B is matrix A with an extra column with
%    The C-th column of A binned into N bins of similar size.
% breakpts is a (N+1)-long row vector with the breakpts of the bins.
%
% A is a matrix. 
%   Consider the values in column C of A.
%   We want to split them into N classes of about equal size.
%   These classes are numbered 1 to N inclusive.
%   Each point is given a number saying which class it is in.
%
%   E.g. A = [1   2   3
%             1   3  -9
%             2   6  10
%            -7   1   0]         
%  
%     then B = addcoarsecol (A,2,2) gives
% 
%   E.g. B = [1   2   3   1
%             1   3  -9   2
%             2   6  10   2
%            -7   1   0   1]
%                 ^   
%                 |___ This column got binned into [2,2], [3,6]
% 
%
% Dinoj Surendran dinoj@cs.uchicago.edu

B = A;
[K,L] = size(A);

vals = A(:,C); 
valsorted = sort(vals); 
breakpts = valsorted([1:N-1]*floor(K/N)); 
if (size(breakpts,1) > size(breakpts,2)) 
  breakpts = breakpts.';                     % breakpts is row vector
end 
breakpts = [min(vals)-1 breakpts max(vals)+1]; 

for k=1:K
  b = B(k,C);
  i = 1;
  while b > breakpts(i)
    i = i+1;
  end
  B(k,L+1) = i-1;
end