# Vectorization, check if points coordinate is exist in an image or no

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Mahsa on 9 Oct 2017
Commented: Mahsa on 12 Oct 2017
Can anyone help me to vectorize this for loop. It is basically ckecking if the x and y coordinate of is one in N matrix or not. Thank you
for i = 1:length(coordinates)
DD = coordinates(i,:);
DDD = N(DD(1),DD(2));
if DDD ==1
%%%if the dicom point is inside the mask
signVector(i) = -1;
else
%%%if the dicom point is outside the mask
signVector(i) = +1;
end
end

Teja Muppirala on 10 Oct 2017
signVector = ones(size(coordinates,1),1);
inds = sub2ind(size(N),coordinates(:,1),coordinates(:,2)); % Convert to linear indices
signVector( N(inds)==1 ) = -1;
Mahsa on 12 Oct 2017
Thank you. I was not aware of sub2ind function.

Andrei Bobrov on 9 Oct 2017
Edited: Andrei Bobrov on 9 Oct 2017
ii = coordinates;
d3 = N(ii(:,1),ii(:,2));
signVector = -ones(numel(d3),1);
signVector(d3 ~= 1) = 1;
##### 2 CommentsShow 1 older commentHide 1 older comment
Image Analyst on 10 Oct 2017
Give us code, or a .mat file, to generate coordinates so we can see what you're seeing.

Image Analyst on 9 Oct 2017
Be careful. If coordinates is an array of (x,y) and N is an array, then you'll need to check N(y, x), not N(x,y) as you have perhaps done. Remember (row, column) is (y, x) NOT (x,y).
Mahsa on 10 Oct 2017
It is true. Thanks