MATLAB: Making column of zero matrix equal to one based on another matrix

matrixmatrix manipulation

Hi ,
I have a zero matrix (A) of size mxn where m in number of observation and n number of feature. I have another non zero matrix (B) of size (mx1) where numbers respresent column in matrix A which should be replaced by one.
How to do this ?

Best Answer

Perhaps you want to set in a row K of A, the entry in column B(k) to one?
%data
  A = zeros(3,3)
  B = [3; 1; 2]       % column index
% engine
  R = 1:numel(B)      % row index
  idx = sub2ind(size(A), R, B) % convert to linear indices into A
  A(idx) = 1
Note that the statement A(R,B) = 1 does not do what you might think it should do.
Related Question