Looping matrice column by subtraction

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Young Lee
Young Lee 2018-10-21
编辑： madhan ravi 2018-10-21
I have a 84x7 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 84x1 vector. How can this be done? let 4x4 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 ]

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madhan ravi
madhan ravi 2018-10-21
编辑：madhan ravi 2018-10-21
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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Young Lee
Young Lee 2018-10-21
thanks for your patience and help :)

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