MATLAB: Basic Vectorization Question (speed required)

bsxfun

I have a 2D matrix of data. I have an index to reduce that 2D matrix to a 1D matrix.
How can I do it without using a for loop? Ie by vectorization as it needs to be super quick.
thanks
Z = rand(5,100); %matrix of data
IDY = randi([1 5], [1,100]); %index into that matrix
X = NaN(size(Z,2),1); %pre allocate
X = Z(IDY,:); %this fails as it does not generate a 1D matrix (vector) as required
this is how I can do it using a loop
X2 = NaN(size(Z,2),1);
for i = 1: size(X,1)
    X2(i) = Z(IDY(i),i);
end

Best Answer

Z = rand(5,100); %matrix of data
IDY = randi([1 5], [1,100]); %index into that matrix
X = NaN(size(Z,2),1); %pre allocate
X = Z(IDY,:)
X3=Z(sub2ind(size(Z),IDY,1:size(Z,2)))
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