Find the position of the first non-zero value in a matrix

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Giannis Nikolopoulos 2021-4-30

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评论： Giannis Nikolopoulos 2021-5-1

Hello, I have the matrix of the image below and I want the position of the first non-zero value of the columns 2 until the end

i used the cumsum expression, it finds the first non-zero values:

out = mymatrix(cumsum(cumsum(mymatrix~=0)) == 1)

but when I do the find((mymatrix(cumsum(cumsum(mymatrix~=0)) == 1)) the result is not the desirable

Has someone any idea?

thanks in advance!

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KSSV 2021-4-30

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A = rand(10) ; 
idx = randperm(10*10,80); 
A(idx) = 0 ; 
iwant = zeros(1,10) ; 
for i = 1:10
    iwant(i) = find(A(:,i),1) ;
end
iwant

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KSSV 2021-5-1

Hi yes you are right, sometimes it will not run. When there is no non-zero element in a column the positon will be empty and in that case it will trhrow werror.

I am creating a demo random data for shwoing the solution to problem. To keep zeros randomly, I have used randperm. You can apply the solution to your data striaghtaway.

Giannis Nikolopoulos 2021-5-1

Thanks for your answer!! finally worked!!

best

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