Matrices

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Alan
Alan 2011-12-30
I want to perform a Principal Component Analysis (PCA) and it is need that matrix has the same number of rows and columns. However, I got a matrix (1142x2) being that first column is composed by number of molecules and second column, species from plants. So, sometimes I got more than one molecule for each plant . In that way, I need to put all species in the rows (173) and the molecules in the columns (712) and put a value (1) only in the correct position, e.g. The 5 speciehave the substances 171, 300, 530, 700, So I need to put the value 1 in (5, 171), (5,300), (5, 530), so on... In the end, I want to construct a matrix of (173x712) which it possesses only values where there is a substance Someone help me Thanks

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Rick Rosson
Rick Rosson 2011-12-30
Please try the following:
X = [ 5 171 ; 5 300 ; 5 530 ; 5 700 ];
M = 173;
N = 712;
Y = zeros(M,N);
idx = M*(X(:,2)-1) + X(:,1) ;
Y(idx) = 1;
sum(Y(:))
HTH.
Rick

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