loop for finding a threshold and change corresponding number
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hi, i have a dataset in the form [2000x730], where my variable of interest is 730. i want to use the loop and find the following equation.
aa=(data)-min(data)/max(data)+min(data);
which i already did with following code:
[m,n]=size(data);
% aa=zeros(m,n);
for i=1:m;
aa(i,:)=(data(i,:)-min(data(i,:)))/(max(data(i,:))-min(data(i,:)));
end
in second part since i have output file aa[2000x730]. i want to find the number where my data meets the required threshold i-e 0.76,
any idea how to loop for it,
regards and thnx in advance
1 个评论
Guillaume
2017-1-9
Whichever version of matlab, you're using the loop in your example is totally unnecessary.
In r2016b:
aa = (data - min(data, [], 2)) ./ (max(data, [], 2) - min(data, [], 2));
Prior to R2016b:
aa = bsxfun(@rdivide, bsxfun(@minus, data, min(data, [], 2)), max(data, [], 2) - min(data, [], 2));
采纳的回答
Guillaume
2017-1-9
As per my comment to the question, the loop you've shown is unnecessary:
aa = (data - min(data, [], 2)) ./ (max(data, [], 2) - min(data, [], 2)); %in R2016b
I'm assuming that you want to find where aa first crosses the threshold for each row. If not, see ImageAnalyst's answer.
[r, c] = find(aa >= 0.76)
crossthreshold = accumarray(r, c, [size(aa, 1), 1], @min)
更多回答（1 个）
Image Analyst
2017-1-8
Why loop? Why not do it vectorized in a single line:
atOrAboveThreshold = aa >= 0.76;
5 个评论
khan
2017-1-9
Stephen23
2017-1-9
@khan: vectorized code will be faster and simpler than using a loop.
khan
2017-1-9
Image Analyst
2017-1-9
The code I gave you was vectorized. atOrAboveThreshold is a logical vector of 1 or 0 depending on if the element is above or below the threshold. If you want a count of the number above, you can do
numAbove = sum(atOrAboveThreshold);
If you want to extract only the numbers above or below the threshold you can do
aaAbove = aa(atOrAboveThreshold);
aaBelow = aa(~atOrAboveThreshold);
These will have fewer numbers of elements.
If you want to mask the ones below, which will keep the same number of elements but just set the "below" elements to zero, you can do
aa(~atOrAboveThreshold) = 0; % Set below values to 0
You should try to learn about logical indexing. It is one of the most powerful features of MATLAB and the key to writing vectorized code.
khan
2017-1-10
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