# How to get values from index in a matrix?

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Paul Hinze am 23 Jan. 2021
Kommentiert: dpb am 23 Jan. 2021
x = [Structure.GK_10.GA_0; Structure.GK_10.GA_10; Structure.GK_10.GA_20; Structure.GK_10.GA_30;...
Structure.GK_10.GA_40; Structure.GK_10.GA_50];
[row,col] = size(x);
for i = 1:row
not_zero = find(x(i,:) ~= 0);
%DOES NOT WORK val_not_zero = x(i(not_zero,:));
mean_first_15 = mean(val_not_zero(1:15));
end
Hello,
i just want to tranfer the indices into real values again, but how can i do it in a matrix. In this loop i i grab the indices that are not zero in the first row. Then i try to get the values in the next line, but it doesnt work, can someone help me?
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dpb am 23 Jan. 2021
mean_first_15 = mean(val_not_zero(1:15));
Besides Walters correction to index into the x array by row, column, the above will fail if there aren't at least 15 nonzero elements in a given row; to do that you would need to handle that condition.
mean_first_15 = mean(x(i,not_zero(1:min(numel(not_zero),15)));
(I think I counted parentheses correctly... :) )
If that isn't of concern as isn't in Walter's code, then you can eliminate the loop entirely by putting in a NaN indicator for zero--
x(x==0)=nan;
meanx=mean(x,2,'omitnan');
That again, however, doesn't limit the number considered in a row but includes the whole array.

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