aligncenterdata.m.svn-base

a function inside machine learning

function Xc = alignCenterData(X, y) 
%Centers a matrix by taking the alignment mean of each column (feature) of M and 
%subtracting the mean from feature value. 
%
%inputs 
% X is the matrix to be centered
%
%outputs 
% Xc is the centered matrix 

if (nargin ~= 2) 
    disp('Usage: alignCenterData(X, y)');
    Xc = 0;
    return;
end

num_features = size(X, 2); 
num_examples = size(X, 1); 

Xc = zeros(size(X));

%mean of the positive and negative examples 
meanPos = zeros(1, num_features); 
meanNeg = zeros(1, num_features); 

%Number of positive and negative examples
numPos = 0; 
numNeg = 0; 

for j=1:num_examples
    if y(j) == 1
        meanPos = meanPos + X(j, :);
        numPos = numPos+1;
    else
        meanNeg = meanNeg + X(j, :);
        numNeg = numNeg+1;
    end
end

meanPos = meanPos/numPos;
meanNeg = meanNeg/numNeg;


Xc = X - 0.5*ones(num_examples, 1)*(meanPos + meanNeg);