How can I extract the first non-zero in several specific segments of the same matrix?

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Phillip 2013-7-5

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https://ww2.mathworks.cn/matlabcentral/answers/81247-how-can-i-extract-the-first-non-zero-in-several-specific-segments-of-the-same-matrix

I'd like to find the first non-zero in several segments of the same large matrix.

For example: x = [3 2 3 4 5 6 6 8 6 10; 0 0 1 0 2 0 0 1 0 1]';

Now within x(1:3, :) and x(7:10, :) I'd like to extract the first non-zero in the second column and write out the corresponding value of the first column...no idea how...any help much appreciated. Patricia

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Answer 1

Matt Kindig 2013-7-5

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https://ww2.mathworks.cn/matlabcentral/answers/81247-how-can-i-extract-the-first-non-zero-in-several-specific-segments-of-the-same-matrix#answer_90952

ix1 = find(x(1:3,2),1,'first');  %index of first non-zero in x(1:3,2);
x1 = x(ix1,1);  %corresponding first-column value
ix2 = find(x(7:10,2),1,'first');  %index of first non-zero in x(7:10,2);
x2 = x(ix2,1);  %corresponding first-column value