Vectorizing a loop calculation

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Azura Hashim 2018-2-24

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https://ww2.mathworks.cn/matlabcentral/answers/384540-vectorizing-a-loop-calculation

评论： Meade 2018-2-26

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Hi,

Is it possible to convert the loop below into a vector calculation? Thank you.

dataset=table();
dataset.value=rand(30,1);
dataset.time=sort(rand(30,1));
timefilter=dataset.time-0.2;
result1=repmat(NaN,height(dataset),1);
result2=repmat(NaN,height(dataset),1);
result3=repmat(NaN,height(dataset),1);
%Loop:
for row=5:height(dataset)
startrow=min(find(dataset.time >=timefilter(row)));
result1(row,1)=nansum(dataset.value(startrow:row));
result2(row,1)=length(dataset.value(startrow:row));
result3(row,1)=nanstd(dataset.value(startrow:row)) ;
end

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Azura Hashim 2018-2-26

Thanks. Yes nansum and nanstd is not required here. I took it from the code that handles the full size data which has NaNs.

Meade 2018-2-26

The sum, length, and std calculations are so trivially fast that it might be fastest to calculate them for the entire array, then just sort. If this doesn't seem unreasonable for your use, I would use bsxfun or arrayfun on your data, then sort. That would be fastest I think.

That would get rid of the loop entirely.

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