MATLAB: Looping matrice column by subtraction

looping matrice column by subtraction

I have a 84×7 matrices. On the entire column 2 and 4, they need to be subtracted from higher number – lower and loop through the whole 84 rows and put them into a new 84×1 vector. How can this be done? let 4×4 matrix a = [x 3 2 y; x 4 1 y; x 1 6 y; x 2 7 y; x 5 1 y;
             b=          [3-2   4-1   6-1   7-2  5-1]
             b=          [1      3     5      5   4 ]

Best Answer

EDIT 2
a = randi([0 9],84,7) %fake data to test
a1=a(:,2) %column you want to extract

a2=a(:,5) %column you want to extract
a=[a1 a2] %two columns stored in a matrix  , sorry I missed this line which caused the error
idx = find(a1<a2)
a(idx,:)=fliplr(a(idx,:))
b = a(:,1) - a(:,2) % as column vector
b1 = b'  %row vector
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